Blue, can you please check out my post about the aftermarket mufflers. You have have been the most knowlegable Ive seen so far.
http://www.grandprixforums.net/f81/my-04-gt-gets-new-lungs-21892.html
http://www.grandprixforums.net/f81/my-04-gt-gets-new-lungs-21892.html