Duramax vs Cummins: Which Diesel Should You Buy?

Put a GM truck guy and a Ram truck guy at the same table and you can skip the small talk. Duramax versus Cummins is one of the oldest arguments in the diesel world, and both sides have good points.

We sell a lot of both at Cars and Pickups, so we hear the argument from every angle. Here is how the two engines actually compare in today’s heavy duty trucks, and how to decide which one fits the way you use a truck.

The short version

If you want the most torque for heavy towing, a simple inline-six design with a long reputation for durability, and you like the Ram’s ride and interior, buy the Cummins.

If you want more horsepower, a smoother and quicker-revving engine, and the Allison 10-speed transmission, and you prefer the Silverado HD or Sierra HD, buy the Duramax.

Either one will tow more than most people ever hook up. The better question is usually which truck around the engine you like more.

The two engines at a glance

Cummins 6.7L Turbo Diesel (Ram 2500 and 3500)

• Layout: inline six cylinder.
• Current rating: 430 horsepower and 1,075 lb-ft of torque in the High-Output version on 2025 and newer Ram heavy duty pickups.
• Transmission: 2025 and newer High-Output trucks use the TorqueFlite HD 8-speed automatic, built by ZF. Earlier trucks used 6-speed automatics.

Duramax 6.6L L5P (Chevy Silverado HD and GMC Sierra HD)

• Layout: V8.
• Current rating: 470 horsepower and 975 lb-ft of torque on 2024 and newer trucks. 2017 to 2023 L5P trucks were rated at 445 horsepower and 910 lb-ft.
• Transmission: Allison 10-speed automatic on 2020 and newer heavy duty trucks.

Always check the exact rating on the specific truck you are looking at. Ratings change by model year, and Ram has offered more than one output level of the Cummins over the years.

Towing and torque

On paper, the Cummins wins the torque fight by about 100 lb-ft, and torque is what you feel pulling a heavy trailer away from a stop or up a long grade. The inline-six makes its torque low in the rev range, which is why Cummins owners describe it as “lazy in a good way.” It never feels like it is working hard.

The Duramax answers with more horsepower and a 10-speed transmission that always seems to have the right gear. On the highway with a trailer, especially on hills, it holds speed very well and feels quicker.

In real-world towing, maximum towing ratings depend far more on the truck configuration (2500 versus 3500, single rear wheel versus dually, axle ratio, cab and bed) than on the engine alone. If you tow something truly heavy, the 3500 dually with either engine is the right tool, and the engine choice comes down to preference.

Driving feel

This is where most people make up their minds after a test drive.

The Cummins has the classic diesel character: deep sound, strong low-end pull, and a bit more of that “big engine” feel through the cab. Fans love it. Some people find it a little truck-like for daily driving.

The Duramax is smoother and revs more freely, and paired with the 10-speed it feels closer to a gas truck in town. People coming from a half ton often adapt to it quickly.

Durability and ownership

Both engines have strong reputations, and both have many trucks on the road well past 200,000 miles.

• The Cummins inline-six design has fewer moving parts than a V8, and its block and internals are known for being overbuilt. That reputation is a big reason Ram heavy duty trucks hold their value well.
• The Duramax L5P is widely considered one of the most reliable modern diesels GM has built, and the Allison transmission behind it has an excellent track record of its own.

Modern diesels from every brand share the same ownership costs: diesel exhaust fluid (DEF), more expensive oil changes, and emissions components that need care. Whichever engine you choose, a used truck’s service history matters more than the badge on the fender.

Which one should you buy?

Choose the Cummins if you tow heavy and often, you want maximum torque, you value the inline-six’s reputation, and you like Ram’s interiors (the Laramie, Limited and Limited Longhorn trims are hard to beat inside).

Choose the Duramax if you want the smoother, quicker-feeling engine, you like the Allison 10-speed, and you prefer the Silverado HD or Sierra HD, including the Denali and Denali Ultimate.

Still undecided? Drive both back to back. Ten minutes in each usually settles an argument that the internet has been having for twenty years.

Drive both at Cars and Pickups

We keep a deep selection of Cummins-powered Ram 2500 and 3500 trucks and Duramax-powered Silverado and Sierra HD trucks across our Texas locations, stock and custom built. No hidden dealer fees, no haggling, no pressure, just two trucks parked side by side so you can decide for yourself.

Browse our diesel trucks for sale or our dually trucks, and if you are also weighing Ford, read our Power Stroke vs Cummins comparison. Then come see us in Dallas, Austin or Houston.