^^ above.
Couple of other things come into play here.
Transmission was installed with all factory pieces, *should* be within factory tolerances for your new setup- factory never changed differential pinion angle (unless there was a production/manufacturing error) between transmission setups, but you're right to check.
*Assuming* you get your pinion angle within tolerances (2 degrees negative- pinion is poiinting 2 degrees DOWN relative to the trans, basically pull that backwards 4* shim out) and you still have a vibration, the only thing left that has changed is your driveshaft. Have balance re-checked, or if a used yoke was installed, it may be excessively worn. Last but not least, people have reported noticeable effects from deleting the bolt-on tailshaft vibration dampening weight on certain year transmissions. Not sure if yours originally had one or not.
