Not a bad truck until the warranty was up. Before then, the only thing to go wrong was the rear door latch adjustment. It worked well in winter (western Canada), got great highway mileage and was reasonably comfortable. For the past two years the following have gone wrong: transmission replaced at 65K, 4WD position sensor replaced three times, tie rods twice, front hubs once. My mileage is 4/5 highway / 1/5 gravel. Its never been driven hard and has had very little mountain driving. Fit and finish are not great but not bad either. Accessories still all work. I bought the truck after having an Olds Alero and Saturn Ion (both had serious drive train issues). I won't buy anything from GM again.
I have a GMC Sierra I bought second-hand with the optional GFX package. I really like the extra exterior/interior features such as two tone paint, stripe on the side, carbon fibre dash, white gauges etc. At first the 4WD did not work, however after a quick cleaning of the connection from the wire bundle to the solenoid on the side of the transfer case, I have had no problems. It came with the 5.3L aluminum block engine and pulls quite hard. Tow/Haul mode is great for uphill towing. The cab had an annoying grinding noise which was quickly remedied with some hockey tape on the cab door latches. Overall, a great work truck and daily driver.
Second GMC I owned and the "MO" is the same: Things started going wrong, repairs started to add up and had to sell the truck before something serious happened to it. Lots of electrical issues especially with climate control system. Stay away from any vehicle with the dual-zone HVAC. Some of these issues can only be solved via dealership who kills you on parts & labor. Traded it in for a more reliable "American" truck: Toyota Tundra. It is built in San Antonio, TX with American labor & parts. Mine was built in Mexico...go figure!
When I purchased my truck almost 5 years ago, it has had a popping sound coming from the front end. It has been to the dealership 3 times, parts replaced each time. Worked well for the last couple of years, than it has started the popping again. Driver side door sounds like it is falling apart for the last 4 years. Had that repaired before and after a couple of years it is again sounding like it's falling apart. For the last 12 years I've owned 2 GMC Trucks and have enjoyed them. Since this is my second truck and I do enjoy it besides the repeating problems I wouldn't mind owning a 3rd, however the window stickers are a little out of my range now.
I love the truck, but I have had it in the shop many times within the first couple months of owning it. I had to replace the radio, because it kept shutting off. I had to replace the shift cable, because the transmition was slipping. There have also been problems with the front passenger shock, dash, and bed squeeking. Along with wind noise from the front windshield. I have also noticed less fuel economy than my previous 5.3 from 17mpg to 15mpg, and a loss in low-mid range power (not towing).