I purchased my GMC new off the lot. So far I've only logged just over 21,000 miles on it. The only problems have been minor; eg: a mild knocking, a broken seat spring, and somewhat twitchy speedo (possibly due to the subwoofers). Overall the truck has proved to be utterly reliable from a mechanilcal aspect and other the the fuel economy of a big truck, the throaty 5.3L is always fun to floor.
Definitely the dual AC, and back seat which is larger than Ford's and Toyota's.