take the cable off, oil it sufficiently. put it back on the tranny. see if that helps, if not, time to dive inside the bell housing. check the fork, when the car drives does it make a bad grinding noise? if so, it may be the fork is bent. that means take the tranny off the car, replace the throw out bearing, new fork, and put everything back together. if you do this, make sure you mark where the clutch is bolted to the flywheel. mark the holes #1, #2, and so on. if the clutch goes on in a different orientation that it came off, you could have clutch slip. thats just because of the way the clutch wears against the flywheel surface.