I have a 2004 Mustang GT that I just recently bought from an auction, took it in to get emissions tested at the dealership and wast told it failed because of a tune the previous owner had on it( Comm. Fail Reason: Cat. Conv. & 02 Unsupported- Programing Error). Asked the dealership to reflash the PCM and they said that they will not due to a recent situation. I have a SCT X4 and was just going to flash a new tune onto the vehicle, but now I am not sure what to do because it would just overlap the previous tune. The only modifications that would require a tune is a BBK cold air intake and a Borla Cat-Back Exhaust. Any suggestions on what to do, can I put a stock PCM in and just upload my custom tune from SCT.