I cracked a second tailshaft housing 3 weeks ago. I'm finally ready to go tear it apart tomorrow. What I'm gonna do is drop 3 lines. One from the balancer, 1 from the trans tailshaft and one from the rear pinion yoke. Then gonna check it with a laser level to see where the line runs from front to back. I'm thinking on mine that I may be off side to side with my trans crossmember. Also, did you use a new crush sleeve when you swapped yokes? I didn't on mine and that is another thought I had. Maybe the pinion isn't set correctly creating the vibrations. But I'm not getting any groaning noises.

What I guess I'm asking here is, do you think that with all the times that you've had yours apart, that maybe the tailshaft isn't located exactly where it was before all this started, up/down & side to side ? When was the very time you took it apart for this problem? What was wrong then?