2000 LS Manual/Clutch problems

I've got a 2000 LS Sport with Manual transmission and about 115000 miles. I bought the car with 3 miles on it, so I'm the only owner. At about 110k miles, I started feeling what felt like clutch slip from what I assumed to be a worn out disk, so my sons and I replaced the disk and pressure plate with all new OEM parts. The flywheel looked great upon disassembly (shiny - no burn marks - no grease or oil), the throwout bearing was smooth, and there was no galling on the transmission input shaft. Curiously however, the old clutch disk looked like it could go another 50k miles before it needed replacement. There was only a minor coating of rust on the splined hole. Now after only about 5k miles on the new clutch, it's much worse than before - car :confused: slips (trailerhitches) under acceleration in every gear. It really makes driving a worry. Any suggestions?