I think you just answered your own question, it has a Butch's head and R&D pipe. You are going to have to check the jetting to see if it is correct for your pipe and head. You are going to have to check the impeller pitch to see if it is correct for your engine/pipe combo and with any pipe you are turning more rpm's than stock so you will have to have a microtouch rev limiter. Check your electrical box for an aftermarket rev limiter. If you do not have one you solved your problem and because of your non-stock setup you are infact hitting the revlimiter like you keep describing how it feels.