since nothing in the tranny turns , how could it be a tranny problem? Tranny out of car, no vibration. As soon as we put tranny in car, vibratioin starts under all circumstances. Off center? tranny mount? motor mount? I have 3 speed and t5 side by side on work bench, end of input shaft on both are same diameter . pilot bushing is same one that was used for 3 speed. 3 speed had no vibration. i measured length of both shafts . T5 is longer of course, but adapter plate makes up the difference exactly. Clutch disc was inspected during first install, looked good and is same one that was used for 3 speed. also, same pressure plate. Only thing changed was new throw out bearing