Driveline vibration out of now where! Help!

AJ/FormS said
This is your clue right here.
After the trans shifted, nothing changed from the trans back.
At 42mph in second gear, the engine was at about 2500 rpm.
After the shift into third, the rpm dropped to about 1750, and the vibration was waay worse..

So now, run it at 1750 in the other gears and see if the vibration is the same or similar. if it is, then look to the engine or TC....If it is not, then I would suspect the vibration originates inside the trans, and oldkimmer may have nailed it

I did that and its worse in 3rd at the same speed than it is in 2nd at that same speed..I can hold it at 45 in second and its just a steady small vibration, but when it shifts to 3rd, that pulsating vibration kicks in bad! Is this what a bad tail shaft bushing acts like? Never have heard exactly what one does when this goes bad..?