Walk onto any diesel forum on the planet and you'll find a thousand 6.7 Cummins owners arguing about what to do first. The answers tend to be the loudest opinions, not the right ones. Spend money in the wrong order on a 6.7 and you'll end up with a truck that's slower than it should be, less reliable than it could be, and a wallet that's $5,000 lighter than it had to be. We're not letting that happen to you.

Here's the actual right order — straight from a shop that has spent years bolting these mods to customer trucks and watching what works. Five upgrades, sequenced so each one makes the next one better, with no wasted money. Build it like this and the 6.7 Cummins becomes the truck it should have been from the factory. Want it done by humans who do this every day? Send us your build — we'll spec the parts and bolt them on.

Why order matters more than which parts

The diesel aftermarket loves to sell you parts. What it's not as eager to sell you is the right sequence. But sequence is everything, because every upgrade either supports or undermines the ones around it. Skip the fuel supply, and your big-power tune kills the CP3. Skip the air side, and your fueling chokes. Skip the reliability mods, and the whole thing comes apart at the worst possible moment.

The right order isn't a guess. It's protect first, breathe second, fuel third, anchor fourth, tune fifth. We'll walk through each stage with the parts that actually deliver.

Upgrade #1: CP4 protection (or stay home)

If you've got a 2019+ 5th-gen 6.7 Cummins, there's a Bosch CP4.2 high-pressure pump bolted to your engine that's quietly waiting to grenade your entire fuel system. We covered the whole ugly story in our deep dive on CP4 disaster prevention, and the short version is this: nothing else you do to the truck matters if the CP4 takes your injectors with it.

The fix is either an S&S Diesel CP4 Disaster Prevention Kit (cheap insurance — bypasses any debris instead of letting it destroy your injectors) or a full DCR conversion (replaces the CP4 entirely with a stouter pump). For most owners, the prevention kit is the no-brainer first move. For built or tow-heavy trucks, go straight to the DCR. Either way, the S&S Diesel collection has what you need.

This is #1 because every other dollar you spend on the truck is at risk until it's done. Don't skip it. Don't delay it. Don't argue with it.

Upgrade #2: A real lift pump (a FASS)

Once the CP4 is protected, the next move is to feed it — and every other fueling component — what it actually wants: clean, air-free, pressurized fuel. That's a lift pump. The right lift pump is a FASS Titanium Signature Series. Full story in our FASS guide.

Why this is #2 and not #4 or #5:

• A FASS protects every downstream component (including the CP4 you just spent money to protect).
• It cleans the supply, separates water, and pulls air out — three things the OE supply doesn't really do.
• It scales with everything else you'll add. Tune harder later? A 165 GPH FASS is ready. Going bigger? Step up the flow once.
• It makes diagnostics easier — frame-mounted means you can see and service it instead of dropping the tank.

Pick the right flow rate for where you're going, not where you are today: 150-165 GPH for stock to mild tune, 220+ if you're targeting real power. Want help picking? Ask us.

Upgrade #3: An S&B cold air intake (so it can actually breathe)

With the fuel side protected and feeding properly, it's time to open up the airflow. An S&B cold air intake is the cheapest, easiest, highest-impact air-side upgrade on the 6.7. Full breakdown in our S&B intake guide.

Why it slots in here:

• It's a true bolt-on — a Saturday morning install, no supporting mods required.
• It improves turbo response immediately, regardless of whether you've added a tune yet.
• It plays beautifully with the next upgrade on this list. A new turbo behind a stock airbox is the definition of leaving money on the table.
• The filtration upgrade alone is worth it long-term — better protection for your turbo and engine.

Run the dry PowerStack if you want set-and-forget; run the cotton if you want maximum flow and don't mind oiling it on schedule. Either way, you're feeding the next upgrade properly.

Upgrade #4: A Fleece Cheetah turbo (the heart of the build)

This is where the build stops feeling like a stock truck with mods and starts feeling like a built truck. The Fleece Cheetah is the drop-in replacement turbo every 6.7 Cummins owner should know about — we covered the whole story in our Cheetah guide.

What the Cheetah does that makes it #4:

• Spool faster with the billet compressor wheel and Fleece's recurve work.
• More top-end airflow where the stock turbo runs out of breath.
• Lower EGTs under tow — real margin when the pyrometer matters.
• Drop-in fitment — same actuator, same exhaust brake, same charge pipe routing. You're not redoing other work to install it.
• Sounds like a Cummins is supposed to sound — the kind of upgrade you hear before you feel.

It slots here because steps 1-3 set you up to actually use the turbo. Drop a Cheetah on a stock-everything truck and you'll feel the gains; drop it behind a CP4 prevention kit, a FASS, and an S&B and you'll feel them plus have the supporting hardware to grow into a serious tune.

Upgrade #5: Tuning (the multiplier)

Now — and only now — does it make sense to add a tune. With the fuel system protected, the lift pump feeding clean fuel, the air side opened up, and the right turbo bolted on, a tune is the multiplier that turns all that supporting hardware into actual horsepower and tow capability.

A few rules for tuning right:

• Buy from a tuner who supports the platform deeply — not a one-size-fits-nothing seller.
• Match the tune to your supporting mods. Don't run a 200 HP add tune on a stock-injector, stock-pump, stock-everything truck. Match the math to the hardware.
• Plan for multiple tune levels. A drive-mode for towing, one for daily, one for fun. Use the right one for the job.
• EGTs are king. The best tune in the world is the one that keeps you safe on a long grade with a trailer. Monitor it.

Need a tuner recommendation? We'll point you at the ones we trust based on what you're trying to do with the truck. Tell us your goals and we'll match you to the right tune.

What about the 2019+ flat-tappet conversion?

If you've got a 2019+ Ram Cummins, there's one additional reliability item that belongs on your radar: the Hamilton Cams flat-tappet conversion kit. The 5th-gen trucks have shown a recurring cam-and-tappet wear issue, and Hamilton built the fix. We walk through it in detail in our Hamilton flat-tappet guide.

Where does it fit in the 5-step order? Functionally, it sits alongside the CP4 protection at step #1 — both are reliability mods for the late-model 6.7 that you want done before the engine has a chance to tell you it needed them. If you're already going in for cam work, valve work, or any front-cover job, do them at the same time. Browse the Hamilton Cams collection for the right kit.

What we'd skip (or delay) on the first round

For the sake of completeness, here's the stuff that's good but isn't on the first-5 list — and why:

• Aggressive exhaust work — fine after step 5, but you're not making power from sound alone. Don't lead the build with a 5" turbo-back.
• Cosmetic stuff — wheels, lights, badges — buy what you love when you can afford it; just don't fund it with money the engine needs.
• Suspension lifts — great for the truck's intended use, but they don't make horsepower or save reliability.
• Trans upgrades — start coming into play after you've added serious power. Stock 68RFE / Allison units take a beating, but they have limits.
• Built engine internals — for big-power trucks, eventually yes; for the first $5-10k of upgrades, no.

None of these are bad; they're just not what we'd buy first. Build the foundation, then add the flair.

What the first 5 will cost — and what you'll save

Real talk on the budget: this isn't a free build, but it's a smart one. Roughly:

Now compare that to not protecting your CP4 ($8,000–$12,000 catastrophic failure), not feeding clean fuel (early injector death, premature pump wear), or not upgrading the turbo before pushing fueling (sub-optimal gains and EGT problems). The first 5 are cheaper than the alternatives, by a lot.

Pulling it all together — the order, one more time

1. CP4 protection from the S&S Diesel collection (and the Hamilton flat-tappet conversion if you're on a 2019+).
2. FASS Titanium Signature Series from the FASS Fuel Systems collection.
3. S&B cold air intake from the S&B Filters collection.
4. Fleece Cheetah turbo from the Fleece collection.
5. Quality tune matched to your goals.

That's the right way to build a 6.7 Cummins. Five steps. No wasted money. Every upgrade makes the next one better. Browse the full Cummins performance products selection, and if you want a human to spec the right parts, install order, and timing for your year, your usage, and your budget — that's our day job. Send us a quote request and we'll get you on the right path the first time.

Frequently asked questions

What is the single best mod for a 6.7 Cummins?

If you have to pick one, the CP4 disaster prevention kit (or DCR conversion) protects the most expensive parts in the fuel system from the most common way they die. Nothing else on this list matters if the CP4 grenades.

Can I skip the lift pump if I'm not tuning?

You can — but you probably shouldn't. The lift pump protects every fueling component long-term, regardless of tune. Even bone-stock trucks last longer with a FASS feeding clean fuel.

Do I need a tune to feel the Cheetah turbo?

No. The Cheetah works as a stock-replacement turbo. You'll feel the spool and sound improvement on day one. Tuning amplifies the gains — but it's not a prerequisite.

What about transmission work?

Stock 68RFE / 6-speed manuals can take a beating but eventually need attention if you push real power. Stage 1 of a built trans is usually a step 6 or 7, not a step 1.

Should I just do all 5 at once?

If the budget allows and you're doing the install in a single shop visit — absolutely. It's cheaper in labor and you only have the truck down once. Tell us your timeline and we'll spec the bundle.

Build paths by use case (because not every truck has the same job)

The five-step order is the framework. But the specific picks within each step depend on what you're actually doing with the truck. Quick decision matrix:

The daily driver (no towing, no big tune)

Keep it simple. Disaster prevention kit at step 1, 150-165 GPH FASS at step 2, dry-filter S&B intake at step 3. You can skip step 4 entirely and a mild tune at step 5 is plenty. Total spend: closer to $3,000. Total benefit: a 6.7 that lives forever and feels noticeably crisper.

The tow rig (15-25k pounds regularly)

Spec for the work. Lean toward a DCR conversion at step 1 instead of just a prevention kit (you can't afford downtime). 220 GPH FASS at step 2. S&B intake at step 3 — the EGT margin matters when you're dragging weight up a grade. Fleece Cheetah at step 4 — quicker spool helps every shift under load, and lower EGTs are gold for sustained hard pulls. Tow-focused tune at step 5.

The built daily (street truck with serious goals)

Full DCR at step 1. 220 GPH (or larger) FASS at step 2. Cotton-filter S&B at step 3 for max flow. Fleece Cheetah at step 4 — drop-in, supports real power, sounds the way you want. Quality tune sized to your goals at step 5. Round out with injectors from our injector lineup when you're ready for the next level.

The race / sled rig

You're outside the scope of this guide — but the same framework applies. Just multiply: DCR + dual-pump fueling, 290+ GPH lift, custom intake, large-frame single or compounds in place of the Cheetah, and competition tuning. The order doesn't change; only the size of each part does.

Not sure which path describes your truck? Tell us what you tow, where you drive, and what you want it to feel like, and we'll lay out the parts list.

Common mistakes that cost owners money

The five-step path works because it's been proven on customer trucks. The mistakes we see most often happen when owners skip steps or chase shortcuts:

• Tuning before protecting. Bolting a hot tune onto a stock CP4 truck with no prevention kit is asking the truck to grenade. Don't do it.
• Skipping the lift pump. "I'll add a FASS later" is the line every owner uses right before they're replacing the high-pressure pump.
• Cheap intakes. The marketplace is full of $99 "performance intakes." They don't seal, they don't filter, and they cost you money long-term. Spend the real money on S&B.
• Wrong turbo for the build. A massive single turbo on a stock-injector, stock-fuel truck is a lag-fest. Match the turbo to the supporting hardware.
• Tune from a stranger. The diesel tuning market has its heroes and its hacks. Ask around, look at customer trucks, and don't buy unsupported tunes from someone you'll never talk to again.

Avoid those five and you're going to be in the upper percentile of 6.7 Cummins owners — both in how the truck performs and in how long it lasts.

Build it once, build it right

The 6.7 Cummins is one of the best diesel platforms ever sold. With these five upgrades in the right order, it becomes one of the best diesel trucks ever sold. Skip the order, skip the right parts, and you'll be back in the shop wondering why. Start at the top of the list and work down — your truck will thank you for decades.

Shop the Cummins performance products collection at DNR Customs, follow the brand-by-brand deep dives linked above, and when you're ready to pull the trigger, request a quote. We'll get you built right, the first time.