I think your hints are correct, and my assumption about the slip yoke is wrong. Tell me what you think:
It knocks bad in 2Hi from a take off from standstill, as we have discussed.
In 4Hi, it still knocks a little bit. But it is later in the gear, and not nearly as severe, one to three knocks top on full throttle.
In N (on tcase) there are no knocks what-so-ever. Takes off.
Same for 4Lo
So you think this is bearing damage in tcase?
Don't take life to seriously, nobody gets out alive.