Cats replaced solved it. But i had also replaced all o2 sensors, cleaned MAF and new air filters. I did visually inspect for vac leaks and took my stethoscope with a piece of old faucet pipe and listened all over for hissing. It was kinda cool to hear the slight valve train, timing chain and supercharger noises - even listened to the water pump. I learned that trick along time ago with an old mechanic while working on my '67 Camaro. Back then it was listening to the oil pump.