I cut out my cat, and I have a 40 series flowie w/ a 2.5 in. exhaust from the Y-pipe back, I bought a O2 Sim from Summit but now I'm thinkin my gas milage took a dive because of it, could this be? I'm talkin 50 miles on a 1/4 tank intown drivin, if this is the problem I want to put a cat back in but I wanna know what kidna to put in that will flow good but not cause the SES light to trip out. Thanks.