Hey guys, i currently have an 03 sierra 5.3. I have had a efilive tune for a few years now. Current mods, volant cai, 03 z06 cam, dynatech long tubes with gutted cats. I recently tried to put a set of cats on the truck to pass my upcoming e-test. After putting them on the truck started running like a bag. It had no previous issues. I have tried cleaning and checking the MAF, throttle body, checked the FPR. The code it throws is po300. Random cylinder misfire. The check engine light usually flashes when i drive now. When i really get on it hard, it looks like a diesel with a programmer on it. The black smoke out of the exhaust is terrible. It also spews an oily black water out of the tailpipe. I ended up gutting the cats, because they were the improper cats. They were for a 4cylinder car/6cylinder car. Now i have no idea what it could be at this point. I cleaned the 02's as well. The front ones are turned off. I thought gutting the cats would fix the problem, guess not. I am changing the plugs tommorow, just wondering if anyone has experienced the black smoke that is plaguing my daily commute. Thanks
cory