Was the kit specifically for the RST?

You should let a new clutch bed-in if you don't have the flywheel skimmed to allow the surfaces to mate [although I would recommed for the cost you should always get the flywheel skimmed if in doubt].

Did you inspect the flywheel? What condition was it in?

Try doing some easy miles on the clutch [say 1000] and see if the problems gets any better. If you have been slipping it a lot then its possible you have scored/burnt the faces and it'll never be right.

Also check to see if there is oil coming from under the car/gearbox to see if the clutch is getting contaminated.

If the above doesn't wok it sounds like its box off time again to inspect and find out whats going on.

It could also be that your clutch is a re-condition and not a genuine one so maybe just can't handle the power Don't forget they are only designed for 130lf/ft of torque.