Sounds like a master. When I knew mine was going, is that i had a 7,000 mile slave in there, and kept on bleeding the clutch, and bleeding the clutch, only to temperarily fix it. then get soft again, well....not soft...but complete "looseness" of any pressure on the pedal.
I've changed 3 slaves, and never changed the master. This time, i'll change the master.
Master cured the issue. I just changed it last weekedn.
Review on bleeding clutch: Fill Resevour, open bleeder and let gravity drain it. When no air and solid fluid coming out, close bleeder. Check resevour. Have an assistant slowly press the clutch pedal down to the floor and hold it. Open bleeder(will be underpressure and will squirt out). Repete 3 times.
'01 XLT disguised as a '03 Fx4 Level II
Big. Loud. Slow. Bright.