Drive line Vibration

I get a fairly heavy vibration that starts around 85mph in fourth or fifth gear and then goes away completly at 135mph in fifth, and does not come back the remainder of the accelleration to 165mph(on the rev limit 3.73's with .79 final gear ratio). Nore is the vibration there before 85mph.

Things eliminated:
Transmission, clutch, pressure plate, flywheel, engine
Drive shaft, changed to FMS aluminium
Wheel balance

Could it be a bent axel? The car has seen slicks.

Thanks for any input