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2015 GMC Sierra 2500 Denali HD review: This is a whole lot of truck

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The Good With its 6.6-liter diesel engine, the 2015 GMC Sierra 2500HD Denali pulls 13,000 pounds, and acceleration is easy to modulate. A collision warning system helps prevent accidents, the IntelliLink head unit offers an easily understood interface with good response, and a 4G wifi hotspot keeps tablets and laptops connected on the go.

The Bad The large size of the GMC 2500HD makes maneuvering tough in tight spaces, and in four-wheel-drive the front wheels bind at steering lock.

The Bottom Line The 2015 GMC Sierra 2500HD Denali adds a few high-tech perks to its old-school work truck frame, helping with navigation and collision avoidance, but the highlight here remains pulling power and load capability.

Visit manufacturer site for details.

7.0 Overall
  • Performance 6
  • Features 8
  • Design 8
  • Media 6

Review Sections

For diesel-fueled cars to pass emissions-muster in the US, they need complex and expensive clean-up systems, which has so far limited their appeal. You don't have to worry about any of that with the 2015 GMC Sierra 2500HD Denali with its Duramax diesel engine, however, as its gross vehicle weight comes in at 10,000 pounds, making it a Heavy Duty vehicle under EPA classifications and exempting it from passenger-vehicle emissions rules.

Despite that classification, the Sierra 2500HD's Denali trim means stitched leather over the dashboard, leather-covered power-adjustable seats, a navigation system, Bose audio and enough charging ports for a Best Buy's worth of gadgets. Equipped as a mobile office for contracting executives, it features the latest version of OnStar with its 4G Wi-Fi hotspot, and plenty of room on the console to perch a laptop.

2015 GMC Sierra 2500 Denali HD
In Denali trim, the GMC Sierra 2500HD comes standard with crewcab and 6.5-foot bed. Wayne Cunningham/CNET

The Sierra 2500HD goes for a base price of $33,545, but kick it up to Denali trim and you're looking at $54,545. The Duramax Plus diesel package, the four-wheel-drive option and a few other sundries brought the example I drove up to $65,165 delivered. You won't find the GMC Sierra 2500HD in the UK, as this truck is just too big to fit in England, and it is only available through third-party importers in Australia.


The Sierra 2500HD impressed me at first because of its sheer size. The top of the grille comes up to my chin, and I could barely see over the bed. At almost 20-feet long, the Denali models come standard with a crewcab and 6.5-foot bed, the grille and wheels shining with bright chrome. LED running lights ring the square headlight enclosures and big trailering mirrors stick out a foot on either side.

Running boards made it possible for me to scale the more than 2-foot climb into the cabin, and little steps cut into the rear bumper's corners help with bed access. Beyond the Sierra 2500HD's high sides, the extreme suspension lift raises the whole vehicle, putting the roofline at 6.5-feet high.

This truck uses traditional body-on-frame construction with leaf springs supporting the rear axle, a type of suspension developed in the Middle Ages. The suspension lift is there to take the Sierra 2500HD Duramax's rated 2,793-pound payload.

2015 GMC Sierra 2500 Denali HD
The Sierra 2500HD's grille is a cliff that hampers close-up forward visibilty, Wayne Cunningham/CNET

Maneuvering the Sierra 2500HD is a challenge. In a typical underground parking garage in San Francisco, I had to make multipoint turns to avoid scraping pillars and other cars. The back-up camera is a great help in this situation, as were the front- and rear-quarter sonar distance sensors, which activated a graphic on the instrument cluster showing how close I was to obstacles. The mirrors offered some low-tech support to help me keep an eye on the truck's sides, their upper flat sections augmented by lower bubble mirrors. Additionally, those mirrors fold flat at the touch of a button to help squeeze through tight spaces.

A truck the size of the Sierra 2500HD could certainly benefit from high-tech maneuvering help, such as a surround-view camera system.

Big torque

The standard Sierra 2500HD comes with a 6-liter V-8 gasoline engine, good for 360 horsepower, but the Duramax Plus package brings in a 6.6-liter turbocharged diesel V-8 with significant power improvement and likely better fuel economy. GMC's diesel makes 397 horsepower and 765 pound-feet of torque. The diesel also means a six-speed automatic transmission from heavy-duty driveline equipment maker Allison, which features manual gear selection to complement its park, reverse, neutral and drive settings.

2015 GMC Sierra 2500 Denali HD
The Sierra 2500HD is exempt from passenger car emission regulations due to its classification as a heavy duty truck. Wayne Cunningham/CNET

Even with all that torque, GMC tunes the Sierra 2500HD's accelerator for light tip-in. Sitting high up in the cab with the diesel clattering away, it took about an eighth push into the accelerator travel to get moving. That tuning is a positive, preventing unintentional running over of worksite equipment or coworkers. Being a diesel, redline sits at a low 3,450 rpms.

That torque means pulling power, and the Sierra 2500HD with the Duramax engine is rated at 13,000 pounds.

On the freeway or crawling over a dirt field, it was easy to modulate power with this diesel. Merging onto the freeway, a solid foot on the pedal made the Sierra 2500HD accelerator as well as the average passenger car.

Not surprisingly, given the truck's suspension architecture, it bounced severely over bumps. But calling out the Sierra 2500HD for its ride quality wouldn't be fair, due to the fact that it is a work truck, and the ride will change substantially when carrying a couple of thousand pounds in the bed.

An optional four-wheel-drive package let me switch between two-wheel drive, four-wheel-drive high and four-wheel-drive low with a dial on the dashboard. In four-wheel drive, the steering binds up with the wheel cranked over, limiting power. For maneuverability, I kept it in two-wheel drive most of the time, especially as u-turns often turned into three-point turns.

Given the Sierra 2500HD's size and power, I wasn't expecting much from the fuel economy, so was pleasantly surprised to see it come in at an average of 16.5 mpg for highway and city driving. That would be a terrible number for a passenger car, but I was expecting worse. However, carrying a significant payload and towing will certainly decrease that number.

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