[98redformula]

I believe your car has a t56 transmission, correct? If so, there is a bushing in the extension housing that keeps the clearance between the yoke and the extension housing tight to keep the yoke straight and concentric around the tranny output shaft. Now excess clearance between the yoke and bushing will allow vibration to occur. If you have a problem with the clearance that is causing the vibration, it can be due to either a worn bushing, a worn yoke, or both. So there are a few possibilities that would cause you to have the vibration after switching the transmission and/or drivershaft. Most likely, both the yoke and the bushing on your original equipment are worn. If so, then you would still experience a vibration by swapping the tranny and using your original driveshaft due to the worn yoke. If the ebay tranny didn't have the bushing replaced (which I wouldn't know), then the worn yoke would be compounded by a potentially worn bushing. Now to the swapping of the 01 aluminum driveshaft...If you swapped the 01 driveshaft into your original tranny, then you would likely still experience a vibration due to the worn bushing in your tranny, but it would likely be decreased because though the bushing is worn, the clearance between the "newer" yoke and the bushing would be tighter than that of your steel driveshaft's worn yoke. This is consistent with your post above indicating the vibration decreased when you swapped the driveshaft. Have you tried the 01 driveshaft with the ebay tranny? In theory, this would be the best combination to determine if this is your issue. I hope this helps.