possible master cylinder problem? please help (for a friend)

[98tadriver]

My friend and I installed a new spec stage 3 clutch and an upgraded slave cylinder in his 99 SS with 20k miles. the slave is bled and the clutch is great. heres the problem-

after about 600 miles, it was getting tough for him to shift

when the car is off, it shifts fine, shifts into reverse

when its running, its really tough to shift it, and impossible to shift into reverse

we bled the slave again and there was no air in there at all. if the clutch was defective like the one i had before, it would roll if i started it in gear with the clutch in. but its fine.

so im gonna say its time for a new master cylinder.. Any ideas?

[JSPERFORMANCE]

or it has a pilot bearing issue or the new clutch clearance is tight and when it heats up it creates more drag on the disc

[98tadriver]

pillot bearing is brand new and clearance should be good, its the same setup i used in my car. and it does it when its cold too.. the thing that gets me is that it was fine for 600 or so miles. i doubt the clutch is defective because it would either be completely engaged or blown to pieces