I've seen several reports of people saying they're losing power with catback systems on the 5.0 S550's. One guy dyno'd before and after going with Stainless Works and he lost 10 HP and 5 ft/lbs and it also caused his A/F mixture to run super rich at higher RPM's. Just a heads up for those with the early itch to start modding before the aftermarket really knows what the heck they're doing.