Here's the thing and I am outta this nightmare. If it's shootin ducks at high RPM (and it is) the mutha frigger is RUNNIN lean. PERIOD, end of discussion. Now, as to why is anybody's guess. Ignition not burning the fuel properly at high RPM? Valvetrain not allowing a complete burn? What the hell ever, the sumbitch is leanin out. That's the bottom line.