Scan for CEL codes and post the exact codes. It may be sometime else besides the mileliminators. May want to consider new mileliminators if it shows P0420 and P0430.
www.mileliminators.com
If it were me, I would remove Bank 1 (or Bank 2) Lower O2 sensor and see if it drives better. If it drives better, you know it is a plugged main cat. Don't drive more than a few minutes, due to hot exhaust going to who knows where (rubber tubing, wiring, etc.).
I think you can buy a "universal" main cat for about $80. Just need to weld it in (or direct fit is $175). I would not gut the main cat. Too much for the po-po not to notice. Good luck.
