I just went thru the same issue just this past tuesday,I changed out the slave as my was leaking when i pulled the boot back.but that didnt fix the problem so i pulled the tranny and saw what the problem was instantly,1 of the springs in the little helper springs had popped out of the clutch disc. Will also add that the car would idle fine and it made no noise at all while running,even when i pushed the clutch in.I would drop the tranny and check the disc.