Annoying Rear End Vibe

[454c20]

Well I narrowed down my vibration at speeds over 55+. It seems to be coming from the back of the truck somewhere as I can duplicate it on jackstands.

So far, I have swapped the rear rims/tires, had a entirely new driveshaft made and balanced (old one was bent), and I just pulled the rear apart to check it over. All the bearings look fine. It seemed both axle shafts had some excessive runnout so I replaced those as well. I'd have to say after all that there is little to no change in th vibration.

What else can it be? The only things I havent physically touched is the actual rear end housing and tailshaft bushing in the transfer case.

Any thoughts? I'm getting tired of putting money into it w/o any changes.