3.0-liter Duramax or 6.6-liter Duramax: Which Is Best for You?

When buying a new truck, there are two questions you’ll ask yourself: gas or diesel, and 1500 or 2500? If you are doing a lot of towing, then diesel is a no-brainer, and Chevrolet and GMC both give the freedom to choose either a Silverado or Sierra 1500 with the 3.0-liter Duramax turbodiesel, or a Silverado or Sierra 2500HD with the 6.6-liter Duramax turbodiesel. But which one is the best option for you? The Fast Lane Truck (TFLtruck) recently put a 2025 GMC Sierra 1500 AT4X AEV Edition Duramax against a 2025 Chevrolet Silverado 2500HD Trail Boss Duramax in a towing test.  

The GMC Sierra 1500 Duramax 

The first truck in the test was the 2025 GMC Sierra 1500 powered by the 3.0-liter Duramax inline-six turbocharged diesel that puts out 305 horsepower and 495 lb-ft of torque and is mated to a ten-speed automatic transmission. While that horsepower number is lower than the gas 5.3-liter V8’s 355 horsepower and the 6.2-liter V8’s 420 hp, it’s the torque number that really stands out, which at 495 lb-ft is 112 lb-ft more than the standard 5.3-liter and 35 lb-ft more than the 6.2-liter.  

The Silverado 2500HD Duramax 

When you are talking about torque, though, there isn’t much that doesn’t have a fuel booster attached that will out-torque the 6.6-liter Duramax V8 turbocharged diesel in the 2025 Chevrolet Silverado 2500HD Trail Boss tester. It makes a respectable 470 horsepower and a massive, draw-dropping 975 lb-ft of torque. Depending on trim levels, MotorTrend has performed 0-60 runs between 6.5 and 7.1 seconds, which is faster than many sedans.  

The Denver-100 Mile Per Gallon Loop 

The fellas from TFLtruck drove the trucks—which had roughly 4,000-pound trailers attached—on the outlet’s famous “Denver 100” mpg loop. The Denver 100 is usually 111 miles long, hence the 100; in this test, they went 115 total miles. The test was a highway loop around Denver, Colorado, that saw the vehicles used for towing at speeds from 65 up to 75 mph. At the end of the loop, they pulled up to the same gas station and used the same pumps to accurately calculate how much fuel was used over the 115 miles.  

Tow Mirrors Versus Cameras 

One of the first things that both drivers noticed pretty quickly was that the Silverado 2500HD comes standard with big tow mirrors, while the Sierra 1500 does not have these mirrors standard. However, when using the turn signals, the truck’s Rear Side View camera made seeing around the trailer easier when changing lanes and maneuvering. While tow mirrors are more essential if you are going to tow quite a bit, Chevy and GMC both have you covered with tons of camera viewing options on the 1500s to keep you out of harm’s way.  

Easy Peasy, Lemon Squeezy 

Both the Sierra 1500 and Silverado 2500HD were able to pull the 4,000ish-pound trailers with very little effort. The driver of the 2500HD said that even though his 24-foot trailer was noticeable when he was speeding up, the truck felt solid and handled “like it’s on rails.” The driver of the Sierra 1500 AT4X AEV did mention that when the wind picked up, he could feel it pushing the trailer around a bit, forcing him to react. However, it wasn’t dangerous or sketchy, just something to note. At the halfway mark, the Sierra 1500 Duramax was displaying an average of 13.7 mpg, and the Silverado 2500HD Duramax was displaying 11.1 mpg.  

Wind Had a Little More Effect on the 1500 

Both drivers discussed the ways in which the trucks drove throughout the 115 miles. The Sierra 1500 had a little bit of trailer sway from time to time, but because the truck was still so large with the AT4X AEV off-road package, it sat 1.5 inches higher than a normal Sierra and felt planted and completely at ease. While the driver knew he was towing and had to adjust his driving style, there was plenty of power and torque as well as size to compensate.  

The 2500 Was a Bit More Proactive 

The driver of the Silverado 2500HD remarked how smooth and reactive the truck felt. The transmission was “grade shifting,” which helped keep the truck in the torque band. The driver said, “I feel like this truck is really in tune with what I wanna do. It’s comfortable, it’s stable, it’s helping me slow down; it’s really quite good.”  

Payload and Towing Capacities Specific to Each Truck Tested 

Although they are in different size classes, both trucks are very capable. However, when comparing the two specific trucks and their payload and towing capacities, the Sierra 1500 AT4X AEV Edition had a payload of 1,048 pounds with a max towing capability of 8,000 pounds. Those numbers are lower than other Sierra 1500 trims simply because the AEV is a genuine off-road truck that features underbody protection, steel bumpers, rock sliders, and more. The Silverado 2500HD Trail Boss is also an off-road trim that has a payload capacity of 3,129 pounds and a max towing capacity of 18,500 pounds.  

How Good Was the Fuel Mileage? 

At the end of the 115-mile test, both trucks were filled to their maximum diesel capacities and the official calculations were made. The Sierra 1500 Duramax took 8.056 gallons for an average mpg of 14.3 towing a roughly 4,000-pound trailer. The Silverado 2500HD Duramax needed 9.744 gallons of diesel fuel, which means it averaged 11.8 mpg towing a similarly sized trailer. 

Is Towing Important to You? 

While you should have a good idea which truck suits your wants and needs better by now, let’s break it down a little more. The 2500HD can tow a fifth wheel, which then increases its towing ability from 18,500 to over 21,000 pounds. However, the 2500HD is a much bigger and longer truck when driving around town and parking in parking lots (or parking garages), which would give the edge to the 1500.   

Priced Surprisingly Similar for Different Use Cases 

When it comes to price, you might automatically think that a Silverado 2500HD is way more expensive than a Sierra 1500, but is that necessarily the case? If you take a 2025 Chevy Silverado 2500HD WT with the Duramax, 4WD, crew cab, and standard bed, you are looking at a base MSRP of $63,085. With a Duramax, crew cab, standard bed, and 4WD, a 2025 GMC Sierra 1500 SLE has a base price of $59,185. That’s only a $3,900 difference. When you consider that the towing capacity of the GMC Sierra SLE is 8,700 pounds compared to 18,500 pounds for the Silverado 2500HD, you can see why the 2500HD may be worth it, depending on your needs. 

Why Choose Valley GMC?

At Valley GMC, we pride ourselves in offering the best sales and service possible. With dozens of new and used vehicles available, our incredible sales team and finance department can help you find the best truck for you and your family. And our fantastic service department will work hard to maintain your vehicle to the highest standards. We look forward to serving you.