2024 GMC Sierra HD AT4X Diesel Takes On the World’s Toughest Towing Test

It was just last year that GMC introduced its first off-road-focused HD pickup truck, the Sierra HD 2500 AT4X. They soon went one step further with the Sierra HD 2500 AT4X AEV Edition, which included additional off-road components from American Expedition Vehicles, such as heavy-duty skid plates and stamped-steel powder-coated bumpers with a design that increases approach and departure angles, and the winch ready front end. 

The Fast Lane’s dedicated truck site TFLTruck already tested the model’s extensive off-road capabilities. Finding it to be quite capable, they started asking the question: Is this the pickup truck that can do everything? That led to a more specific question: Because a major point of an HD truck is increased towing capacity, is the Sierra HD 2500 AT4X AEV Edition still a suitable towing vehicle, or has it sacrificed towing ability with all of its off-road hardware, including its lifted stance and 35-inch tires? On paper, the truck has an 18,400-pound maximum towing rating, but for TFLTruck, the question was not how much it can tow but how well. To get an answer, they decided to give it what they call the “world’s greatest towing test”. This involved hitching the Sierra HD 2500 AT4X AEV Edition to a trailer holding a CAT skid-steer loader, amounting to about 11,000 pounds, and driving it up and down what they call the “Ike Gauntlet”.

What TFLTruck dubs the “Ike Gauntlet” is an 8-mile portion of the I-70 interstate that crosses the continental divide in the middle of the Colorado Rocky Mountains. It has a 7% grade with a top elevation of 11,158 feet above sea level. “Ike” comes from the Eisenhower tunnel that is within the route, which of course, was the nickname of the President who approved the interstate freeway system, including I-70. As TFLTruck states: “If a pickup truck does well here, it will tow your trailer with ultimate confidence anywhere.”

The HD 2500 AT4X AEV Edition naturally comes standard with 4WD and is available with either the 401-horsepower 6.6-liter gas-powered V8 or the 6.6-liter DuraMax turbo-diesel V8. As this is a towing test, they chose the Duramax, which is rated at 470 horsepower with a stump-pulling 975 lb-ft of torque. Between the engine and transfer case is an Allison-branded 10-speed automatic transmission. The Gen-Y-branded hitch TFLTruck uses for their towing tests has height adjustment ability to bring the trailer connection to a proper level from the truck’s elevated ride height. 

No Drama Uphill

The truck had two occupants and no additional payload in the back, so the 6.6-liter Duramax had no trouble pulling the 11,000-pound trailer up the 7% incline or dealing with the thinning air at 5-figure elevation levels. To quote TFLTruck: “This GMC Sierra HD was confident, stable, and quiet on the way up the mountain.”

Steady Downhill

When heading downhill, power is less of an issue than control and the ability to avoid riding and overheating the brakes. They prepared for the descent by setting the cruise control to 50 mph and shutting off the adaptive cruise ability. The truck’s Tow-Haul mode was set, as was the exhaust brake. With these settings, the brakes were only applied once, and that was near the beginning of the descent. The exhaust brake did the rest to keep the truck and trailer at a steady 50 mph. A Trailer Brake Gain digital readout that appears on the HD’s driver information panel enabled the testers to monitor the brake usage.

The Pickup that Can Do Everything

TFLTruck already tested its extensive off-road ability and its accommodations for regular truck use. It appears that this could indeed be the pickup truck that can do everything. We all want our pickup trucks to be capable, but if you want your truck to be the most capable, you simply have to visit Buick GMC of Rochester, get behind the wheel of a GMC Sierra HD 2500 AT4X AEV Edition. If you’re looking for the perfect one or want to customize, we can certainly find or order one for you.