Check your clutch for proper adjustment and gap through the inspection hole in the bell housing. If all looks good there, then spray some CRC Brake Kleen on the clutch through the inspection hole to make sure there's no oil contamination, then check to see if it's still slipping.
Check out these links for how to properly adjust your clutch:
1. http://pantera.infopop.cc/eve/...0045562/m/125102346/
2. http://www.panteraplace.com/page124.htm
3. http://www.spacecitypanteras.com/techinfo/Clutch/
And after you've done the above, if it's still slipping, you need a new clutch.
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