I've had this problem (wheels lock up when in reverse and in 4 wheel drive) for quite some time but, since I rarely use 4 wheel drive, I've put off having it checked. With winter coming on I thought that it's timely to have the dealer check it. They did agree that it did lock up but advised me that GM was aware of the problem and that a service bulletin had been issued and that nothing could be done. Apparently another issue that GM has chosen to ignore. That's the first issue..

The second complaint is that, since I made an issue of this with the dealer (Lambert Buick, GMC in Cuyahoga Falls, Ohio) they now have the ability to charge a diagnostic charge. GM builds a problem into their vehicle, which they choose to do nothing about, then the dealer charges you because you bring it up.

My transfer cases on my 2005 Envoy seem to go very quickly. Funny thing is I RARELY every need to put the car into 4WD or any other drive other than regular 2 hi. I was in a parking lot at work when I went to go back out of the space and the wheels seemed to lock up. I looked down and the car was in 4 hi. How did it get there?? So I shift it into 2 hi (for normal driving) and the car shakes as I try to drive forward and sounds like the exhaust is about to fall off, thats how loud it was sounding. So I turn it off, and then re-start it. It goes about 100 feet and tries to die on me. I pull it into a parking space. read this part carefully.... I am in PARK. I let my foot off of the brake and the SUV of death lunges FORWARD about a foot!!!! I WAS IN PARK!!! I turned it off and it was towed. The dealer had it for a long time and said NOTHING is wrong. HUH???? A few weeks later it starts acting up again and is taken to the dealer it was bought off of and they find out that it is the actuator assembly in the transfer case. HUH?? what is that. So they fix it and I am on my way. Until it decides to go again.