Cummins or HEMI? Choosing a 2027 Ram Heavy Duty Engine for Western Slope Work

Two engines, one decision, and people get it wrong all the time. People buy the diesel because the tow rating is bigger, or skip it because the sticker is smaller. Neither is the question. Here is what each gives you, what each takes away, and the factor that outweighs the tow chart.

Why does altitude matter more than the tow rating?

Because a tow rating is a number on paper, and altitude happens to you every time you leave the valley. A naturally aspirated gas engine loses roughly 3% of its power per 1,000 feet of elevation. It has to: it makes power by burning fuel with the oxygen it can pull in, and the higher you go, the less oxygen is in each cubic foot of air. A 100 horsepower engine at sea level makes about 85 at 5,000 feet, and no trim level fixes it.

Run that out to where the roads around here go. A 6.4L HEMI at 11,000 feet is down roughly a third of its power. The 405 horsepower in the brochure is a sea-level figure, not the one doing the work when you crest a pass with a trailer behind you.

A turbocharger largely fixes this. As ambient air density falls, the turbo raises boost, forcing denser air into the cylinders than the atmosphere is offering. The Cummins doesn't shrug off elevation completely, but it holds far more output than any naturally aspirated engine can. This is the strongest argument for the diesel in mountain country, stronger than towing capacity.

What does the Cummins actually give you?

Torque, first and mostly. The HEMI makes 429 lb-ft. The Cummins makes 1,075. That is not a percentage improvement; it is a different category of engine, and it is what you feel the moment a loaded trailer meets a grade. Everything else on the spec sheet follows from it.

Then the turbocharger, which is the mountain argument above. Then the exhaust brake, standard on the Cummins, carries the retarding load on a long descent so your service brakes aren't the only thing between you and the bottom. The tow rating is downstream of all three. It is a symptom of the engine, not the reason to buy it.

Ram labels its 2027 heavy-duty towing and payload figures preliminary. The 37,020 lb 3500 figure comes from Ram's 2027 press material; Ram's own retail page still lists 36,610 lb. The 2500 HEMI's 4,580 lb payload requires the $835 Payload Upgrade Package. The 3500 HEMI's 7,580 lb payload is a dual rear wheel Regular Cab. Maximums require specific configurations.

Read that torque row again, then read the payload row. The engine that makes 1,075 lb-ft also weighs more, and every pound of engine is a pound you cannot put in the bed. On a 2500, that is 590 lb of payload gone. Say it both ways, or you haven't said it honestly. It is not a Ram quirk; it happens in every brand's heavy-duty lineup, but it is a real trade-off, and it catches people out after the sale rather than before.

On a 3500, the trade changes shape completely. The Cummins adds nearly 19,000 pounds of rated towing for the same money, at a cost of 1,120 pounds of payload. If you pull a large fifth-wheel or a loaded gooseneck, that is not a close call. Ram's chart also requires a fifth-wheel or gooseneck hitch above 20,000 lb, so 20,000 lb is the practical ceiling on a bumper-pull regardless of engine.

Is there a standard-output Cummins?

Not in the pickups, and this trips up shoppers reading older content. The 2027 Ram 2500 and 3500 pickups offer only the High Output Cummins. There is no SO versus HO decision to make. The 360 horsepower, 800 lb-ft standard output Cummins exists only in the 3500, 4500, and 5500 Chassis Cab. When shopping for a pickup, the diesel choice is one engine at one price.

One more correction. Some sources still list the 6.4L HEMI at 410 horsepower. That was the 2025 figure. Ram's 2027 material says 405.

What does an exhaust brake do, and why doesn't the gas truck have one?

The Cummins comes with a standard Diesel Exhaust Brake, the feature Western Slope owners care about most. Lift off the throttle, and a butterfly valve closes in the exhaust, sealing the system. The engine now pumps against heavy backpressure, converting the momentum of truck and trailer into heat inside the engine instead of your brake rotors. The rig slows on the engine. Your pads stay cool.

That matters because of brake fade. Push rotor temperature high enough and the pad material vaporizes, forming a gas layer between pad and rotor that destroys braking effectiveness when you need it most. A long grade with a heavy trailer produces exactly that.

Diesels need an exhaust brake because they have no throttle plate. A diesel controls power with fuel, not airflow, so when you lift off it pumps air freely and gives very little engine braking on its own. A gas engine is different: lift off a HEMI and the pistons work against a closed throttle, pulling vacuum and producing meaningful engine braking with no extra hardware. The HEMI is not missing something. It gets the same effect for free, though it does not match a dedicated exhaust brake on a long descent.

What kind of fuel economy should you expect?

We won't give you a number, and here's why. No heavy-duty pickup has an EPA fuel economy rating. Pickups over 8,500 lb GVWR are exempt from EPA fuel economy testing and labeling, so no certified figure exists for a Ram 2500 or 3500, or for any competitor. Every mpg number online for these trucks is owner-reported, not measured to a standard.

The one official range datapoint Ram publishes is the 2027 Power Wagon with the Cummins: a 31-gallon tank and approximately 600 miles of range. We are deliberately not turning that into an mpg claim, because Ram did not. Same on maintenance: service intervals and diesel exhaust fluid consumption for the 2027 trucks come from third-party compilations we could not verify, so ask our service department for the Mopar schedule.

The honest verdict

The HEMI is genuinely the right truck for some people, and we will tell you so. If you load the bed heavy and tow moderately, the 2500 HEMI's 4,580 lb payload beats the Cummins by 590 lb, the 3500 HEMI's 7,580 lb beats it by 1,120 lb, and you keep $12,995 in the business. A contractor working the valley floor with a full bed and an occasional equipment trailer is better served by the gas truck, and there is no shame in that math.

Most of our Western Slope towing customers still land on the Cummins, and it's the road, not the brochure. It is 646 lb-ft more torque where a grade asks for it, a turbocharger that holds power at elevation while a naturally aspirated engine gives up a third of its output by 11,000 feet, and an exhaust brake that keeps the descent off your rotors. That describes every serious tow route out of Montrose.

Bring us your trailer weight, your hitch type, and the roads you drive, and we will put you in the right one, not the expensive one.