I bought this car (2006 GT Auto) used from a dealership in May. It was bone stock down to the filter. First mod was an O/R X Pipe. Ran a 14.1 in the quarter mile in hot, humid weather. (I live in FL. Always hot and humid this time of year.) Next mods were SCT Tuner and JLT CAI from AmericanMuscle. Ran a 13.89 on 87 street tune. Next, I purchased and installed MAC long tubes and pro chamber with stock mufflers. Also ordered a re-tune from Bama. Before I could take it to the track, an opportunity came up for me to swap my stock mufflers for the Roush Extreme Performance catback. Ran 13.8 three times with the best being 13.81. The numbers on my timeslips were very similar to the previous ones before the long tubes and pro chamber. I was not expecting to shave off anything ridiculous but I did expect to see more of an increase than .08. I plan on contacting Bama on Monday and getting their opinion. But, in the mean time, I was wondering what other people's opinions were. Is this a normal gain on a N/A car? I am happy with the exhaust note. A much better combination IMO than the x pipe with stock mufflers. I just expected more performance gain.