About 6 months ago I put on a pypes o/r x-pipe and cat back. I bought some mil eliminators from american muscle and put them on also. Since day 1 of putting on the exhaust my ses light has been on and when I check it, it gives me a code for bank 2 running lean. Now, it still gives me the same code, except bank 1 is running very rich (by looking at the plugs) and that code does not come up. Also my gas mileage went from 29mpg on the highway down to 23mpg. I also replaced the O2 sensors, but that didn't help anything. Also did a tune-up and new coil packs since then (one of the packs went bad), and that didn't help anything.

Anyone have advice on what might be wrong? Also, I am replacing the clutch in a couple of weeks and thinking about going to a high flow catted system since I'll have the x-pipe off anyways. The pypes x-pipe hangs very low and I've heard that the UPR hangs a little higher. Is this right? I want to lower the car in a couple months and put on a different suspension, and don't want the exhaust scraping the ground all the time. Also, does anyone know how much going to a catted system will affect how loud my exhaust is?

Car is a 2003 GT with the only mod so far being the exhaust.