2012 GMC Sierra Denali 4×4 Diesel Review

I had a big ‘ol manly Texas truck this week, the 2012 GMC Sierra Denali 2500 4×4 with the Duramax diesel and 6-speed automatic transmission. I can’t say I enjoy driving any three-quarter ton or larger truck, they are just so big and ride so rough, but I get so many questions on them, I just have to do it.

For those that need to tow or haul heavy loads, this truck is a contender. This Sierra Denali came completely loaded with everything you can think of including the navigation system, a power sunroof, heated and cooled leather seats, rear camera, 20” aluminum wheels, chrome running boards, and even a heated steering wheel.

The Duramax performs well and the 397-horse 6.6-liter turbo diesel is quieter than I remember it from past experience. The Allison transmission is smooth and changes fluidly, unlike the last Ram I had which seemed to slam into the various gears. From a dead stop, the 765 lb-ft of torque will get this mammoth truck rolling quickly and deliberately.

For those of you who tow, the Sierra Denali has impressive numbers. For a conventional towing setup, you can pull 17,000 pounds and if your trailer is a 5th wheel, it goes up to 21,700 pounds. That edges out the Ford F250 by a scant 100 pounds and slays the Ram HD which is rated at 17,000 pounds with a 5th wheel setup.

Also for folks who tow, stability control, trailer sway control, and diesel exhaust brake are standard, and an integrated trailer brake controller is available as an option.

The interior of the truck is very nice, the seats are comfortable, and everything is super easy to operate. This truck has a large amount of interior cubby holes and numerous cup holders for all occupants.

As is typical of any truck this size, the ride when not towing is rough and you feel every bump in the road. It just has to be this way to have a truck that can tow 10 ½ tons. I think the GM fully-boxed steel frame makes this truck stiff and rigid, but at the same time very stable. The independent front suspension on this truck gives it responsive steering for a truck of its size.

In the ongoing battle between diesel trucks, I think the Ford Super Duty holds an advantage in quietness, fuel economy, and without a doubt in back seat room-which is a little cramped in the General Motors entries.

Speaking of fuel economy, the Denali got 15 consistently in town and with the 3:73 rear-end this truck has, I got 20 miles per gallon highway at 65-miles per hour.

I’ll let you truckers go out back and argue which is best between the Duramax, the Powerstroke, and the Cummins.

I can tell you the GMC Sierra Denali 2500 diesel is a very capable truck.
What I liked most: The torque and quietness of the Duramax.

What I would change: For sure, more back seat room.

MSRP: $62,124.

Fuel Economy: 15 in town, 20 on the highway.

2012 GMC Sierra 2500 in a few words: A very capable truck with impressive stats.

[starreview tpl=16 post=1161 style=’oxygen_gif’ size=’24’]

  1. Frank Ashby 5 years ago

    Excellent review, Mr. Reynolds.
    I am about to retire and have been shoppping for a vehicle which my wife and friends alike can tour North America and tow @ ~38 ft. fifth weel trailer to vacation of Hunting/Fishing locations. As I am entering retirement, fuel economy, maintenance, and longevity are exceedingly important. As such, how I resolve the three trucks you mention? Are there on-line forums, reviews which address these issues? can you recommend dealers in Texas which have specialists who address the towing specifications (rear differential)?

    • Michele Sanders 5 years ago

      Frank, good to hear from you! If I were you, I’d go with the Ford at least today. The 6.7 Diesel is a great engine, very quiet, lots of horsepower, and Ford does a great job with their factory towing system. I also think the have the best towing mirrors out there.

      Let me know which Texas market you are in and I’ll recommend a good dealer for you! THANKS for listening to the show!

      Jerry Reynolds “The Car Pro”
      President, Car Pro Radio Networks

  2. Brian 5 years ago

    I found this review very helpful. I’m also looking at buying a fifth-wheel that my truck can pull without taxing my truck. I’ve got the 2012 GMC Denali 2500 diesel and keep reading varying towing capacities for fifth-wheels. Differences such as 15,800 to 17,800 to 21,000lbs. And differences from SLT to Denali, where the Denali is rated about 2,000lbs less than the SLT. I’d like to think my stock Denali would tow 21,000lbs of fifth-wheel, but I’m not sure.

    Any other comments on the weight differences from your experience? And are there any suggestions on boosting that tow rating?


    • Michele Sanders 5 years ago

      Brian, good to hear from you. Honestly, I don’t think you’ve got enough truck, but I don’t know which rear end you have to say with certainty.

      Generally when you get over 17500 or so, I recommend a dually for the stability, which means you’d have to go to a one ton, which I suspect you need.

      Click here: http://www.gmc.com/trailering-towing/towing-charts.html

      That may help you, I sure hope so. THANKS for listening to the show!

      Jerry Reynolds “The Car Pro”
      President, Car Pro Radio Networks

  3. Shaun 3 years ago

    just wanted to add my experience with the 2012 2500 GMC Sahara Denali diesel with the Allison transmission. I first purchased my first Dinali in 2012. It made it home Manasses far as it got. In 2012 the 6.6 Duramax has had some issues. These issues have been kept very quiet my first Duramax was the 2012 2500 GMC Sahara Denali with a Duramax and Allison transmission fully loaded. On my way home with that particular truck is starting to suck and coolant fluid so much so that you had to go back to the dealer and they told me that the heads were not bolted down correctly or that the wrong head gasket was used during the installation. After careful consideration of what to do with the dealership there were three options rebuild the motor put a new motor in or find a vehicle that matched that particular vehicle that I ordered . I chose to have them find a brand-new 2012 GMC Sahara Denali. So my second 2012 GMC Sahara Dinali lasted 70,000 miles and then the hands lifted. It is now March 2015 and the truck is still a Second dealership because the first dealership it was that for four months could not fix the problem and created more problems with the vehicle. It just so happens I have an on board – camera that runs off the battery I was able to record the entire process of the first dealerships work. If anyone knows about how to remove head from a diesel engine the first thing that is done is both batteries are disconnected. My dash camera would not be operating if the batteries have been disconnected. Long story short the truck has gotten major electronic and fuel issue still the oil pan has been removed and it will pump has been replaced the heads have been replaced turbo now wines and I get diesel exhaust in as a cab. General Motors is working with me on getting this truck fixed but it has been a major headache because this vehicle is not just my play toy it is also my work truck and has caused major issues for my business.
    Just wondering if anybody else has a problem with the 2012 Duramax diesel engine in the GMC Sahara Denali

    • Michele Sanders 3 years ago

      Quite a story Shaun, I hate to hear this, I have not heard anything like this before. I hope GM can get to bottom of it and get you fixed up once and for all! Thanks for listening to the show.

      Jerry Reynolds, President
      Car Pro Radio Network

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