Two problems related to noises during shifting have been reported for the 1996 GMC Sierra. The most recently reported issues are listed below.
While towing trailer with 2 quads (4 wheelers) on expressway with a group of CO-workers, I was attempting to pass another vehicle when my truck would not shift into passing gear. It made a loud "reving" noise and began rapidly decreasing in speed. I pulled off the expressway bringing the vehicle to a complete stop. I then gradually accelerated and shifted manually, but was only able to acheive 1st gear. I had to have the vehicle towed 150 miles to my house where it still sits three months later with only reverse and 1st gear operable at this time.
Consumer was traveling about 25mph on highway and went to make right hand turn, and rear end shifted and vehicle started making funny noises. Transmisiion started slipping, and vehicle wouldn't go into shift at all.