Drive Shaft Vibration?
 

I just got my 88 Mustang running (5.3 4L80 S475 turbo swap) I'm getting a drive shaft vibration about 60 MPH. When I built the rear end I replaced the drive plate with a standard type 1350 yoke. I want to try to cover the basics before I go back to the drive shaft shop. I rotated the tires, checked pinion angle (-2 degrees). Anyone have any ideas??

how do you know or what makes you think the vibe is caused by the drive shaft ?
i would reduce pinion angle and go more towards zero, if it's easy to change. at highway cruise it's light load and in my opinion there's no where near enough force to rotate the pinion upward like when launching the car, i would set pinion angle to -0.5° and see if that helps at all first.

if you assembled and press the ujoints into the drive shaft yoke, you might have messed them up. it can be easy to loose a roller bearing out of them or even have a broken one inside of them and you won't know until you pull them and inspect. also for some joints there are spacer shims under the cap that can fall out and if you assemble without them you can have movement inside the joint which would cause vibes.
if possible measure runout on the axle pinion yoke and on the drive shaft near the axle, it's not that uncommon for the pinion yoke on the axle to have runout and cause vibration.