not really a muff problm as much as a tuning problem... flowmaster mufflers or magnaflows or borla are good mufflers to use.. go with a single chmber flowmaster like a 10 series....a fuel injection system has the ability to adjust fuel trims only so much.. thats were a tuner comes in.. a system running to lean or over rich will loose power.. it needs to be corrected with some type of tuner sct is the best but if all your gonna do is intake and exhaust then go with a superchips....