Make sure the u-joint’s are phased properly. I know that’s necessary but couldn’t explain.
Someone here maybe or a driveshaft shop can explain.
It needs to be balanced anyway at a shop.
They can tell you if the shafts still good too.
Replace your center bearing. The one you can buy new is too loose so it needs to be shimmed tight in the bracket.
Guess they can break, seem to remember someone taking about that. Corrsioon would certainly be a problem but fatigue is a well.