The issue that you are experiencing with your exhaust system is not due to the fact that you have a Flowmaster muffler, but rather that you have the incorrect series of Flowmaster muffler installed for your application. The 40 Series muffler that you have is quite aggressive and not especially tow-friendly. Here is a link to the recommended mufflers and kits that we offer for your truck. Our 50 Series HD mufflers are better suited to the needs of tow vehicles. Best of luck to you!