If the Dyno is showing slip, then your motor is actually making more then it showed. It's quite possible you are overwhelming the clutch springs and pack. Especially if it's some junk set up from Tusk or something similar. Many of the generic clutches out there don't really hold more then 65-70 hp even with what they call HD springs. Hit up Driveline, Redline, or Fast for a quality set up. If that doesn't fix it, throw a lock up at it.