Sounds like your pawl and quadrant (the plastic, junk, self-adjusting mechanism up under the dash) may be getting stripped. Could be a stretched cable too. Hopefully not though. Go out there, and pull up on the clutch pedal, and see if it'll adjust.
If the cable or the plastic junk is toast, replace it with a metal quadrant and adjustable cable. There are a few options here, but whatever you do, don't get new plastic pieces - upgrade to metal.
__________________ 1992 Deep Emerald Green Mustang GT Hatch, 5 speed, 2.73s, Mac fenderwell cold air intake, '93 Cobra MAF, Mac 70mm throttle body & spacer, Explorer intakes, Mac unequal headers & offroad pipe, Magnaflow catback, Walbro 110lph fuel pump, Jet adjustable FPR, MSD Blaster coil, Accel 8mm wires, FRPP aluminum quadrant, UPR firewall adjuster, stock cable, Granatelli upper control arms.
Waiting to go on: Granatelli lower control arms, and GT40 Iron heads! | 
Help Please Clutch problem 
