1999 Chevy S-10 clutch slips

I recently replaced the clutch in my 99 chevy s-10. I drove about 50 miles and it started to the same thing before I replaced it. It started slipping. The clutch pedal comes all the way to the top with no play. I can shift it into gear but it won't move. The clutch, pressure plate and release bearing were replaced. It seems to build up pressure as I drive.
Jim Crowell