on my old Z I had a one piece drive shaft and some vibration. I also knew it had to be the drive shaft considering ever bushing from subframe to Diff was new and everything was tight. No play anywhere in the driveline. I messed with it for some time. Clocking the driveshaft differently made some improvement. This next part sounds redneck but I put a hose clamp around the drive shaft. Marked it and went for a test drive. Slowly did that over a few weeks rotating the screw part of the clamp around. Eventually I found the point where I couldn't notice the vibration. The plan was to have it balanced later but ended up getting rid of the car before.
