Driveline vibration problem

[snipescastle2]

Hello all! Happy Thanksgiving!
I've been having a strange driveline vibration in my truck lately. It starts at 65 mph and gets worse at 80 mph. I had my driveshaft balanced the other day and that didn't do it. When I let off the accelerator it stops, get back on the gas it comes back. I'm going to re-balance my tires again and see if that helps, the engine was totally balanced before I put it together, and I have the correct flexplate. Could a bad torque converter cause this vibration? It could be I through a weight off my tire/tires or maybe even a bad tire. Just looking for suggestions. One note, I did notice a lot more backlash on my pinion yoke when I re installed the driveshaft, I'm starting to wonder if I have the right crush on my pinion crush sleeve after I rebuilt my differential? Could the pinion bearing be causing the vibration? I recently changed the gear oil in the rear end and added the posi additive and I didn't see any weird wear marks on the gear teeth.
Perhaps I should buy another crush sleeve/ pinion bearing/seal and re torque it again? Let me know what you think.
Have a great turkey day!
Ben