Let's talk about exhaust drone...

@Hogleg whatever works out with all these suggestions, I wish you the best. The O/O I drive for has some jerry-rigged muffle system that I'm not sure I should talk about, but... its been mentioned above, to a degree.
That's a helluva ride there, man.. I drive something similar and I love the purr, I guess, LoL!

 

I love the straight pipe sound on my 7" straights but they are 13'5" tall from the ground. I here ya on the drone noise inside the cab, mine was about 1500 rpm, so I kept it below that. Anyways, since I'm in Cali, I had to install the retrofit DPF and it quieted down. Drone noise gone. Many that I knew install a shorty muffler but punched the center baffle out. Drone noise disappeared but still had the deep straights sound.
P.S. The shorty muffler install was under the cab just after the bottom elbow, usually next to the utility box(behind). Also with the shorty muffler install, DOT wouldn't mess with you for loud pipes.

 

@rollin coal

 

Here's a thread on this;
http://www.thetruckersreport.com/truckingindustryforum/posts/5219676/

 

Found this too;
https://www.googleadservices.com/pa...ahUKEwiE2_idsabRAhVKylQKHUkJDlkQwg8IHQ&adurl=

 

@Hogleg these shorty mufflers from this thread I started a few months ago are good mufflers but came from Pittsburgh Power and are way overpriced. But I do like them a lot better than the Donaldson M100463's they replaced. You can cut Pittsburg Power out of the picture and source the muffler direct from the manufacturer if you want. They will make a muffler any size you want. See my last comment in the thread for info on the manufacturer.

 

Or maybe Heavy Duty MFG.com: 800-241-0551 PN 1-501-18A or 1-501-24A. I can not tell you exactly how any of the three I mentioned would work for you but will just add this. Some straight through mufflers are open center like a car glass pack. Installed backwards they have better flow and are a little louder. Turn it around and you have a different muffler.

 

I thought about turning mine around backwards but I didn't want them obnoxiously loud. I'm glad I didn't because I've heard my truck straight piped and hated it. It has a nice deep tone to it now not too loud, just right. People tell me all the time here recently when it's just parked and running that it sounds great and ask what kind of motor it is.

 

@Hogleg this pic shows my Y and how it ties together under my truck. I painted the mufflers with black high temp paint to help inhibit rust. Like I said really could have used some mufflers shorter than these but it worked out. The piece of flex attaching to the muffler on the right in the pic. Originally the Y there went into the muffler from the factory. That was a necessary "engineering change" to tie it together.