Can anyone think of, or has heard of, any reason why going from an off-road X-pipe to the stock H-pipe (with cats) would cause performance issues? The battery was disconnected for 20min and it seemed to help a bit, but it still acts a bit strange under load. Like it hesitates and sputters a bit above 1500-2000 RPM. Any info appreciated. This is on a 96GT 5spd.