Thanks for the suggestions.
A blocked Cat or O2 sensor are both on my list of suspects. Any idea on the best/quickest way to test to be sure?? I guess I could disconnect the O2 sensor and see if there is a change...I was also thinking that the coil may be breaking down. Does that sound possible?? It almost feels like the timeing doesnt advance..
What is really strange is that it runs so strong right up to 4000 RPM, and sometimes will go all the way to redline and seem OK. Thanks ...