Did a google and got this donaldson muffler is the best that money can buy. . It still gives a good rumble but cuts all the drone out. . and I know trust me i tow 17k daily... .
dayuum they went up in price when i bought mine. . but well worth it
It's a muffler. Many, many big trucks run them as factory equipment. They typically flow just as good, and better in some cases, then most aftermarket mufflers. You and I would probably want the M90535 from what I can tell.
Not my truck but a good sound clip-
YouTube - Dodge 51" Donaldson 5" muffler