Ok, my check engine light has been on since I bought the car used a year and a hlaf ago.  I had it checked after I bought it and the codes were p0420 and p0430 both catalyst effeciency codes for bank 1 and bank 2.  I did worry too much about it because I was getting good gas mileage.  Recently my gas mileage has gone to crap, I just filled up a day ago and now I am at 3/4 tank and only been 81 miles (WTF?), check the codes again and its just the same two codes.  Whats the deal here?  Could there be another reason why I am getting bad gas mileage?  i have done nothing to the car except a custom short ram intake, and throttle body heat bypass.  I am thinking of taking it to the dealer and seeing whats up.  Anything yall can think to try before I go get ass raped by the dealer?