My friends 98 Z28 M6 has some issues with the clutch. It seems to slip only when ya first get into the gear. When you're entering the gear, and lay on the gas it will sometimes rev up. But if you've already been in the gear for a minute or so then slam on the gas it will take off no problem. So, I believe it's hydrolic issue, not actual clutch. 98 is one of the ones with that damn slave cylinder inside the bellhousing isn't it

Whats the best way to go about diagnosing if its slave/master cylinder or actual clutch issue? The car's already got that little hole drilled on the floor to mess with the hydrolics, but thats about all I know about that "mod"