Ok, I have a 04 corvette z06. Before i got the car the owner put long tube headers high flow cats and crossover. before he had the all 4 o2 sensors before the cats causing the rear o2 sensors to not read the cats i thing he also had a programmer on it 2 but no way to be sure. Causing the check engine light to come on for low cat efficiency on both banks. since then i have rearranged the exhaust to read the cats but im still getting the code. Is it possible that the high flow cats are still the problem? if so is there a way to get around it? Also i just put a k&n intake on the car and it feels to me on the freeway going 70 in 6th it feels like its surging and or like just taping the brakes barely. could have some of the oil from the k&n got onto the mass air flow sensor causing it to surge?

thanks for the help scott