I'm puttin a 5.7 in my GTX and this is what I am going to use
www.corsaperformance.com

This is based on the recomendation of the car builder that is helping me on this project. he says he had an 06 Charget R/T from a client to install a new muffler system so it would sound "badder" than the stock one. They tried 4 major brands, flowmasters,etc, and they all did the resonation thing. The Corsas made the sound right and completely eliminated the resonation.

Worth looking into after an experience like that.