Love everything about this muffler! Sitting on a near stock Chevy HD 6.0 with 4.10 gears, it's very close to the sound and growl of the #low@master 40 series, but at a constant cruising speed. it's not that loud! I installed dual 3.5" crampons and then rerouted to a 4" rear exit tube. In fact, I got 1mpg fully loaded with a trailer hauling rolled steel at 70-75 mph. The big 4-door HD gives me an AVERAGE 15.6mpg - 285/75/16 in all terrain, with the Escalade electric fan π Not bad at all