I agree with the others above. The manual transmission can't slip like an automatic can. If it is in gear, which I'm sure it was, then the "slipping" was either the clutch plates, or the tires.
The clutch plates are pretty resiliant. I took the clutch plates out of my stock Z06 after a year of driver's education events, and two race seasons to replace it and found that it looked almost brand new.
As suggested above, a good test for clutch slippage is to do a rolling WOT with the car in gear and closely watch the tach. If the tach goes up fast but the car doesn't feel like it is accelerating normally, then your plates are slipping. But, I'm betting they (and your tranny) are fine.
