I just replaced my OEM muffler with one of the Aero 4040's muffler. Beautiful piece of equipment, polished stainless steel, actually a real shame to hide it under a motorhome. I'm not sure of all the claims, ie, better mpg, more hp, what it did do is made my little 275 hp Cummins sound like 500 hp!! LOL!! It is not opressive, nice pleasing, deep, sound. I bought mine from, Parley's diesel.com.
'05 Monaco Beaver 400 Quad SLD 400hp C-9 Caterpillar
2014 Grand Cherokee, Limited, diesel
Katie-Doberman Pinscher, Tigger, yellow Tabbycat.