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

There can be many reasons to purchase an HD truck, but one of the primary reasons is towing. However, half-ton trucks like the Sierra 1500 can also have pretty impressive towing capacity. Many truck shoppers may wonder if the trailer is within the smaller half-ton truck’s maximum capacity, if the half-ton truck is all they need, or if they would still be better off with an HD model. The Fast Lane Truck YouTube channel created a test to answer or at least address these questions, and GMC of Rochester tells you what the outlet found.  

The Test 

TFL Truck accessed two nearly identical trailers, a GMC Sierra 1500, and a Chevrolet 2500HD. The editors charted a highway course that consisted simply of the 470 toll loop around Denver. The 115-mile route consisted of basically unbroken, uninterrupted driving at highway speeds. They ran the route simultaneously, comparing notes as they drove. The test started at a fuel station (where they topped off) and ended at one, so they could get an accurate fuel mileage rating for each vehicle on the drive.  

The Trucks 

The GM trucks selected were not optimized for towing ability, though the powertrains were. The Sierra 1500 was an AT4X with the AEV Edition Package. Basically, this truck was optimized for off-roading with a large assortment of AEV (American Expedition Vehicles) aftermarket parts, including special front and rear AEV bumpers, additional skid plates, rocker guards, and 35-inch all-terrain tires, among other items. The engine was the 3.0-liter Durmax turbodiesel inline-six, producing 305 horsepower at 3,750 rpm and 495 lb-ft of torque at 2,750 rpm. The Duramax was mated to the GM ten-speed automatic. 

The Silverado 2500HD was only slightly off-road focused, with the Trail Boss trim featuring 4WD, Rancho twin-tube shocks, and 20-inch wheels with all-terrain tires. It is directly comparable to the Sierra 2500HD 2500 AT4. It also had the best powertrain for towing: the 6.6-liter Duramax turbodiesel V8 that produced 470 hp at 2,800 rpm and a stonking 975 lb-ft of torque at 1,600 rpm. It was paired with an Allison ten-speed automatic transmission and had a 3.42 rear axle ratio.  

The Trailers 

Both models pulled a nearly identical empty InTech 24-foot, dual-axle toybox. The only real difference was a few more options on the trailer pulled by the HD, including a roof-mounted air conditioning unit. As such, the trailer pulled by the 1500 was about 4,000 pounds, while the HD’s trailer was about 4,500 pounds. Though not heavy, the trailers were long, wide, and tall. Again, the whole point of this exercise was to tow trailers well within the 1500’s 8,700-pound towing capacity to see if there was still a reason to select the HD model. 

The Experience 

On the road, the 1500 driver expressed a wish for the tow mirrors that are standard on the HD, as the trailer was fairly wide to see around with the standard mirrors. However, the camera systems helped, including the side rear images that appeared on the digital display when the turn signal was engaged. 

The 1500 driver felt that his truck was pretty stable on the drive, although wind gusts hitting the empty trailer could be felt. With about 2,000 more pounds and a longer wheelbase, the HD had a stability advantage and was hardly taxed by the trailer’s weight.  

The 470 loop does not reach the mountains west of Denver, so no severe grades were encountered in this test. The 1500 driver opined that if there were, the greater power of the HD truck might be more acutely felt.  

At the end of the drive, the 1500’s trip computer registered 15.0 mpg, which was slightly over the calculation of 14.3, with an average speed of 54.9 mph. The 2500HD trip computer read 11.9 mpg with the same average speed, and the calculation was nearly the same at 11.8 mpg. So, for this test, there was only about a 2.5-mpg difference for a heavier truck with twice the displacement, pushing a bigger hole in the air.

With that little difference, it seemed like the HD truck should be considered for its increased stability and greater reserve capacity should towing needs increase in the future. Of course, there is the purchase price difference. There is plenty of overlap in the 1500 and 2500HD price ranges. Because the 1500 was an AT4X AEV Edition, it was approximately $10K more expensive than the 2500HD Trail Boss. Looking at a mid-grade SLT trim level for both, a comparably equipped Duramax 2500HD would cost about $15K more than the 1500. As the drivers pointed out, when not towing, the Sierra 1500’s more compact dimensions make it a bit more convenient around town.  

As usual, the choice depends on individual use. If the truck is towing significant distances most of the time, the HD may be worth the difference. If towing is only occasional, the 1500 may be all you need. GMC of Rochester welcomes you to test drive both and discuss your towing needs with our sales professionals. In all cases, we wish you happy towing.