not exactly experienced in the driveshaft business.... but, isn't that what a balanced driveshaft is for... it's balanced, no 180 out stuff?
i had a terrible vibration in the car a while back... wouldn't do it in neutral but once i got up to bout 100kph/60mph i would feel it real bad, was totally vibrating the whole car, found out it was just tyre balancing... didn't think balancing could get that violent
another way you could try is maybe jackstands and chocks, drop the driveshaft so no rear end action and just run the engine and trannie and see if it still does it
just a thought
i had a terrible vibration in the car a while back... wouldn't do it in neutral but once i got up to bout 100kph/60mph i would feel it real bad, was totally vibrating the whole car, found out it was just tyre balancing... didn't think balancing could get that violent
another way you could try is maybe jackstands and chocks, drop the driveshaft so no rear end action and just run the engine and trannie and see if it still does it
just a thought