Make sure your clutch fork is still on the pivot ball if the quadrant and cable check out. This is especially important if the car is of higher mileage and the pivot ball has never been replaced since there will be more clearance as it wears, increasing the possibility of it coming loose.
i would check the cable at the pedal first. then check the cable connection at the clutch. if the cable is stretched, get a cable, quadrant and firewall adjuster from maximum motorsports and be done with it. maximum motorsports has the highest quality parts in the clutch cable department. they have done their homework on solving those problems.
well i self adjusted the clutch by pulling up on the pedal, and it was back to normall, them a little while after i did a hard shift and i got floppy agian, but it fells better when its floppy!!! idn....
Sounds like your quadrant is failing. It seems you adjust it to get it proper and under heavy load it looses its adjustment. I would just get a new FWA and Quadrant kit. If you are using a stock cable and its in good shape...keep it.