Vibration issues

Byron,Thank you for your post #7. Helps a bunch. REREAD your last 8 words...You have been doing a lot of u joint and yoke switching around. In the 3rd line you state "I bought a ring and pinion and built the 3.73s THEN THE VIBRATION STARTED"
I might look real close at the u joint straps. There are a lot of them of different styles and sizes. That could of gave you the first time vibration, sent the drive shaft flying, and still giving you the vibration.
Did you say you have solid motor mounts? Just curious. But my real question here is what transmission mount did you put on and when did you put it on?
After breaking two tail shafts (on the track, with a big mess) we found out it was the new polyurethane transmission mount and went back to the original.