I hated seeing that engine light and CEL so much I pony'd up and installed the GSM Cat-Eliminator Sim boxes. It seemed a little steep at $199 but no more problems and I think well worth it. It's way different than what you get with their track mod which is just switches and wires. This actually cleans up the signal it gets from the O2 sensors and tricks the computer to see everything is running smoothly.
Check it out - just another option if nothing else works.
http://www.gsmotorsports.com/Merchan...ode=HMIENGELEC