Motorcycle Repair: Early Sportster Clutch Slipping, castrol gtx, motorcycle oil

Question
1970 XLCH Completely new CCI clutch installed before storing bike all winter---changed oil using Castrol GTX 20W50 Full Synthetic---first time out for ride performs fine but after about 1 hour of hard running a slight momentary "slip" particularly in high gear is felt---feels like tranny is slipping or clutch is dragging---

Answer
I have no experience with CCI clutches but overfilling the tranny will cause slipping.  Also, why are you using full synthetic in the tranny?  Use it in your motor if you want but only use v-twin motorcycle oil.  Use the Harley SportTrans oil in your tranny.