My car's clutch pedal was stickin half way up not just at WOT but just cruisin around town too. I had a theory that it was my slave because I was at a stop light in gear with the clutch pedal in and I was revving it up waiting for the light to turn and the pedal stuck to the floor. Its because when your slave is bad, the part that is flawed causes the sleeve to bind in its bore and not release the pedal when it gets hot like when your revving up your engine.
I bled the fluid, mity vac for air in the lines, changed my master cylinder, nothin worked. So I just changed my slave cylinder and it fixed it.