Thanks Moedip for the suggestions, but the air filter nad fuel filter are new and I have run injector cleaner through several times. The fuese on the OVP is new also. I have considered the OVP, but it doesn't exibit any of the common symptoms of a bad OVP. It idles smooth and no ABS light. Is there a way to check the OVP. I don't want to just start swapping parts. The strange thing is that it run great around town and only has this problem above 4000 RPM. I may have been mis-leading when I said there was a slight vibration coming from the engine when this happens. It is more like change in the harmonic frequency of the engine.