Ok, so I have posted on here that I was having this clunk when I would get to the gas after a stop. Let me start buy saying saying I have wasted TONS of money and countless opinions and finally I have solved the problem. My chain of events... Trans goes out and replaced with a GM trans. After that I had this clunk sound from the rear end and I swore it was my rear diff. The chase began, rear end serviced and carrier bearings replaced...no fix. One tech thought to be leaf spring bushings (the where basicly gone)...no fix. New slip yoke and u-joints...no fix. I had another tech swear it was the rear diff, I just couldn't throw $500 towards something I really felt was not the problem...didn't do it. The FIX...trust me!!! I have a friend that's a parts manager for a local GM dealer and he pulled a GM bulletin from several years ago on this issue. The bulletin states to replace the slip yoke with a nickel plated one...had mine replace but not the nickel plated one. And also put GM Auto Trac II (blue) in the transfer case with this special GM grease on the slip yoke. So I check the fluid in the T-case and low and be hold the tech who installed my new trans must have put regular trans fluid (red) in the T-case...BIG NO NO! I flushed the trans fluid out and added the GM Auto Trac II fluid and loaded my slip yoke with the GM grease and now my truck runs AWESOME no clunk at all!! So before you go and have different opinions just check your t-case fluid and make sure you put the GM auto trac II fluid if you see the red. My truck has 195,500 miles on it and I believe now it will go for a bit longer! There must be something with the blue fluid that really lubricates the gears in the t-case and the GM grease really keeps it soft on the yoke splines. Just had to let all know.