Transmission Problems? Ask a Mechanic for Answers ASAP
There are about 50 service bulletins from GM on these trucks that address a drive-line clunk either when accelerating or stopping. The nature of the drive-line on a transmission and engine with this much torque is to develop clunks apparently.
Is your truck 4wd or 2wd?
Do you have any tires that are slightly larger or smaller than the others?
You can check this by wrapping a string around each tire and making sure that there is no more than a 1" circumference difference between any tire.
Does it sound more like it's coming from the rear or the transfer case?
Does it seem better or worse in 4wd?