I had this problem and I was sure it was the throwout bearing, but on a whim I disconnected the clutch cable at the clutch release lever and sprayed white grease all over it. then I put it back on there, and adjusted the freeplay to factory specs. I had to do this a few times. there was some rust on the operating lever causing it to bind with the cable. but now it feels like a new clutch.
but that doesn't eliminate the possibility of a bad throwout bearing. start with the small stuff though. and since we have mechanical clutches and not hydraulic ones, it's easier cos we don't hafta worry about a master cylinder, slave cylinder, or fluid leaks.