TKO600&Moser12bolt do I need to shim to get proper pinion angle for 69 bird?

[RBR]

I have been driving the bird and i'm trying to work out all the kinks now. I feel a vibration at about 60mph. It goes away at higher speeds and lowwer speeds. Is it common to have to shim the rear end to get proper pinion angle? I have a tremec 5speed and moser 12bolt.
My very crude measuring shows the tranny a little lowwer in the rear and my driveline and the rearend seem equal.
I'm droppinp my drive saft now and attemping to get a better measurement.
Thanks for any replies.