My 40 Chevy/302 GMC/T5/Ford 9" has developed a high frequency vibration around 60 mph, 3000 rpm in 4th and 2000 rpm in 5th.
I vote
NO to it being a failure of the T5 input shaft bearing. The input shaft RPMs are identical to the engine RPMs (unless you have the clutch pedal depressed). So the way I see it, if input shaft bearing failure was the problem, it would have the same vibration at the same RPMs in 4th and 5th gear (or any gear for that matter).
