Bought this truck new in 2004 with 171 miles on it. Since new I have had the rear clunk, oh yeah, it's NORMAL they say. I was sitting at a restaurant on a hill one morning just days before the extended warranty was to expire. I put the truck in reverse and let off the brake and began to roll forward, down the hill. Hit brakes fast. Shifted from Park to Reverse several times. Never felt the truck engage. While sitting there with the truck in Reverse trying to figure out what ot do I finally felt the tyruck engage. Backed up and went to the dealership. They checked the truck and found internal damage to the front differential and they rebuilt and reprogrammed the transmission. Picked up truck and truck would not shift into 4HI, with Autotrac. Took back, checked codes and found transfer case was bad. Put in re-manufactured transfer case. Next day Service Trans light on and codes stored again. Had to repair "NEW" transfer case. Okay. 4 months later oil under truck. Had to repair output seal, covered this time under GM warranty. GM warrants tranfer cases 3 years and 36,000 miles. They don't tell you that, or they didn't me. I found out at the Goodwrench website. A big plus now, the clunk is gone, I think the tranfer case was bad all along.