When you get a muffler installed keep in mind theres a few items that will influence the sound of the muffler:
Length of tail pipe, i.e. if it's cut off just behind the muffler it will be louder, and not as deep (rumble).
Diameter of tail pipe, larger pipe = louder and tinnier sound.
Tail pipe exit point makes a difference to sound in the cab and the added tube to get to the back makes a little more rumble.
I have a DF50 that I originally piped to the stock location, ok sounding.
Moved exit to the back of the truck, less in cab noise, rumble got deeper with more exhaust pipe.
And finally located at back of truck tucked up and behind the trailer hitch angled down and back, nice rumble, no annoying in cab issues.
I also tried different pipes after the muffler, I settled on a 2.5" pipe into a 8" long 3" diameter tip.