I just bought a 2006 K3500 dually to tow a race car hauler. I don't need lots more power, just looking to help a bit on economy and a little bit more power, if that comes with it. I intend a 4" stainless, turbo back single exhaust with a muffler. Those long trips criss-crossing the Midwest mandate that we have the quietest muffler these needs will allow. What do you guys use for good flow-thru, while still being quiet for the long drives.