I purchased my GMC a few weeks ago so far so good. I had a Ford F-350 powerstroke with 7.3. The GMC is small in the inside compared to the Ford. The GMC has a lot better fuel mileage but seems to be too light to handle heavy trailers. It's not short of power it will smoke my Ford easily. My biggest complaint is lack of interior room. GM still needs to do their homework on that. The quality is not matched by Ford or Dodge in the interior and standard accessories, but I think Ford is heavier duty than GM for all out abuse on the farm or on construction sites. In about a year i can tell the truth because I know Ford can hold up. Curious to see if GMC can.
6.6 Duramax and Allison is great combo very strong. Fuel mileage excellent, 15.8 in town 19.6 on highway.
More interior room and rear air vents. No room for larger tires on front.