I recon you should heat wrap your Sport Cat to stop unburnt fuel getting through causing the number 2 hego sensor, (the one after the cat), reading unburnt fuel.

Is the inside of your tailpipe sooted up/black ? I ask this because when i had my sport cat on my last the engine light was on constantly and the inside of the tailpipe was black; since changing to the original cat, no engine light, and no sooty deposit.