I've had this annoying death wobble in my truck for ever and it keeps getting worse.

After doing a bunch of front end work I started to turn my attention to the front U-joint on the drive-shaft that could be causing the problem. But it seams like the Joint is fine though there is an excessive amount of play in the shaft coming out of the transmission.. I can knock it side to side easily.

Is there a seal or bushing in the tail end of an automatic transmission that might have gone bad?
The trans has around 80k on it, I pulled it from a dually camper and swapped it in my regular cab.

Edit: Realized I posted in the wrong section since I have an 88 but w.e question still remains..