you DO NOT need to de-tune your car.. only thing they read with the ODB is that all your systems are ready and your RPM.. you will have to put your stock h pipe on unless u have a catted X/H with good cats... If you fail let me know.. u might have to do a few tricks like pull a little timing .. also make sure you have all your emission stuff on like EGR, Air pump etc
you DO have to de-tune if your o2 sensors or warmers are turned off in the tune
you DO have to de-tune if your o2 sensors or warmers are turned off in the tune
My cars just pullied too, I just threw the stock h pipe back on didn't mess with the tune and passed just fine. This was in January 2013.
and i bet your rears are off