My buddy just installed a SPEC stage 1 clutch in his 96 Z28 and he gets a bad vibration as he lifts off the clutch pedal to get the car rolling from a dead stop. it runs smooth after the clutch pedal is fully released. it doesnt do it as badly while the car is rolling when he shifts to the next gear. its just from a dead stop. this is what I tried already:

engine running, tranny in N pedal out=no vibration
engine running, tranny in N,pedal in= no vibration
engine running, tranny in 1st, pedal in=no vibration
engine running, tranny in 1st, pedal just slightly up=vibration
engine running, tranny in 1st, pedal out, car moving=no vibration
engine running, tranny in ANY gear, pedal slightly up=vibration

 

I believe you're describing clutch chatter. New clutches can be "grabby" causing the chatter. Some clutches get much smoother after around 500 miles of normal driving. My friend's Spec 3 has always had chatter releasing in first gear, even after 20K miles; all other shifts are fine. My street twin was never grabby.

 

you are definately experiencing clutch chatter. Specs are particularly bad about it. It will get better after the "break in" period. But specs have always been known for having clutch chatter. one thing i have noticed that helps is not just riding the clutch out to get going, specs hate to be slipped at all. Just give the throttle a little blip and then let the clutch out. See if that helps at all.

Brent