I read a magazine article where they said poor performance on the KA24DE could be caused by a clogged pre-cat because the factory header rusts and the particles off of it clog the pre-cat. it says an aftermarket header without a pre-cat will fix the problem. I ask because my Altima has the poorest acceleration and no top end. and a scanner read that my catalytic converter is plugged, but my main one is clear. any comments or advice?