I've read allot of the post concerning my problem I need some input on:Just had a SPEC Stage III (alum fly) put in my 2004 ZO6 (10,500 miles) 5/5/05 200 miles ago. It now has a serious vibration 2400 and up that changes which RPM it is more prevalent at. I am currently trying to diagnose where the problem exist. With the clutch pedal pushed to the floor and checking the clutch disc for excessive movement. How much vertical "play"(pushing straight upon disc) and how much rotational "play"(move disc left to right before input shaft moves) is considered acceptable. I think the disc has a problem in the splined hub area. Causing the disc to be off center at different amounts in turn cause my vibrations to change. FYI Had local Chevy dealer replace the clutch(for 200.00 labor) while they were fixing the 3rd gear syncro. It was mysteriously damaged while the left fuel tank was being replaced for a leak.