wont go into gear after about 20 to 25 mile of driving

[chops_dsm]

i just bought a 97 gsx with this problem. when u first start it up and drive for a good 20 min. or 20 miles it wont go into gear anymore. but if i let the clutch off a little then it will go into gear but it will only rev more than go. it seems like there is pressure somewhere that is pushing the slave cylinder too much because its not coming back at all. then i would bleed it to release pressure and the slave cylinder would go back and the car will work good for another 20 min or so. i dont know whats causing the slave cylinder to do that. i swapped a new slave cylinder and same thing. the master cylinder looks fine its pretty new yet too. i adjusted the clutch pedal, slave cylinder and the master cylinder and no matter what the car will not go into gear after a while of driving. i thought that it might be the clutch pressure plate so i put in a new act 2100 pressure plate and street disc and same thing. it had a rebuilt tranny already when i bought it. but my father thinks its not the tranny hes my mechanical and my dads pretty darn good. but we are stuck and frustrated. oh yeah the clutch pedal also gets stiffer too when it wont go into gear. and u can hear the flywheel (i think) rubbing against the disc when u step on the clutch when it wont go into gear. the stick shift wont move at all when u step on the clutch all the way. within the 20 min. of driving it drives fine everything works perfect. but i dont really know why im having this problem. its my first dsm. any help will be appreciated. thanks in advance.

 

[KRRZ350]

Maybe the rubber line is collapsed internal, seen this on brakes many times but never on a clutch, but it makes sense when getting warm and would fit the symptoms. But first I'd check out this:

YouTube - Proper Clutch Adjustment