hmm, Yeah out of balance d-shaft sounds like it could be cause. Also might as well check out all the CV joints and maybe even the wheel bearings. Also fluids swaps may be in order if you havent done them at the intervals. Lots of times fluid leaks or old dirty fluid will cause one the of the diffs/tcase or trans to do things as you've described. Leaning towards those not being the culprit but the truck will love some fresh fluids if the time is near
Anything rotational that takes force will wear obviously and then being to grind/hum/clunk etc etc. Very common, Im sure you will find the issue, just have to put the time and effort in to get - G/L with the diagnosis.