Well I have the Magnaflow highflow cats (removed the 4 stock on a 2004 5.4 liter), borla duals, and a magnaflow X-pipe. The truck was quiet but sounded good at WOT until I added the high flow cats. Now it drones big time if you touch the throttle up to about 2250 RPM. My wife refuses to ride in the truck. So, I am looking for two quiet mufflers to replace the Borlas. Hope you have better luck.