So, to make an excruciatingly long story semi-short, here's what's happened so far:
3.27 gears, car had a mild case of the vibes. Worst around 90 MPH, but tolerable.
PST aluminum shaft - sent back to PST due to incorrect yoke. Had to index my stock shaft because of this (don't ask), and the vibes were a little worse, but still tolerable. Don't think I got the indexing right...
Got the PST shaft back, and installed 4.10's and the PST shaft. The resulting vibration was horrific! Car sounded (and felt) like a prop-driven airplane. Stock driveshaft was a little better
, but basically, nothing touched it. Car stayed in the shop for 1 week.
These guys were so persistent with the problem - several transmission guys, driveline guys, etc. helped with the car. Pinion runout was 0.001". We were going to try to have Ford send a balanced diff/flange assembly, but they don't have those anymore since they've started producing stuff for the '03's (whatever that means). So basically, 2 days of shimming the transmission & diff. snout to change driveline angle, indexing the driveshaft, axles (basically verything that rotates), PLUS installing a '01 axle damper finally got the vibe down to tolerable levels. It still needs some work - now the vibe can be more heard than felt due to the damper, but it's not quite right yet. It's at least 80% better, though.
So, the PST shaft made things worse instead of better - never could get things to work with that shaft. Bizzare.
I don't think it was re-balanced when the proper yoke was installed? Guess I'll just have to send it back and have them check it, huh? Boy, this is the third time.
Probably, the remaining vibration can be tuned out with a small weight on the pinion flange, if I can ever get a good driveshaft in the thing.