86 , 5.0

hi folks, i have a clutch problem thats eating my lunch. i installed a new hi performance clutch, pressure plate, all bearings, new clutch cable, and had the tranny rebuilt, put it all together, and the clutch worked fine, for about 6 miles, the clutch got hard, and i tore it all apart, nothing out of the ordinary, put it back together and same thing, but this time the cable came loose from the fork. i know nothing about the plastic stuff under the dash.. could this be my problem? thanks for any help. mark