[pappyl]

Vibration problems in the driveline have can have many sources - so i'd start with the easiest first:
- balance your tires
- make sure your engine is in tune
- check your transmission mounts (rubber broke)
- check your engine mounts (ie: broken bolt)
- check your springs U brackets
- check your universal joints (4 in my burban)
- pull off your back wheels, check for play in your rear axle (should be very tight - any play= new bearings and possible new rear shaft)
- possible - inner bearings in the differential

note: I ended up changing my bearings - if you tow at all - expect this - keep your bearings and rear fluid up - your axles will be a-ok)