I hanged the u joints in my driveshaft when I had my transmission rebuilt a few years ago. Since then, I have had avery noticablevibration like what you are describing ever since then. I KNOW that is the problem in my situation, because that is all I changed. When (or if) the guy ships my third member to me and I change it, I will take the shaft to a local driveline shop and have it balanced.

I had them build a custom shaft for mebut the damn thing was crooked though, so I must admitI am skeptical about their work. Ever since then I have always just made my own shafts from junkyard units and they have always turned out vibration free. Guess Ive just been lucky on that one...

Anyway, I would suspect tires or driveshaft balance issues.