When my engine is cold it will barely rev above 3700RPM, it is also shudders badly when I go past half throttle. Even when the engine is completely warm it will still sometimes hesitate when I go to wide throttle openings. I've changed the cap, rotor and plugs, wires, and put STP fuel injector cleaner through the system. Didn't really make much of a difference. Any other ideas?? MAF, TPS, O2 sensor??