'98 XJ w/possible clutch problems?!?!

Friend has '98 cherokee 4.0, 5spd. clutch usually works fine but at times seems as if it won't disengage completely when pedal is on floor. pedal always feels firm. shop told me most likely clutch master cyl but I thought that would make the pedal spongy if it was bad??? I was wondering about slave cyl but can't get any answers from people without having it checked in shop ($$$)... Anyone familiar with this???
Jay