Gearing/info seeking

[Lonestar10]

So recent was able to dig my data plate for my rears out of it's paint tomb. Found dealership advertising of 3.55s was wrong. I have 3.36s and 65-67mph is around 1300 rpm and around 70 is 1400ish. I would say my loaded miles is 95% at 70k to 80k lbs flatbed with about 32000=empty weight at 1/2 tanks.

So question is what might a better gear be for my cm871 13sp. With 500hp mm tune. My cruise speed is 65-67mph when loaded and at 80k she feels like a snail getting there and almost any incline or breeze makes her want to go-to 30+ lbs of boost loaded. Winter fuel average is 4mpg.

I did have 2cylinders with bad exhaust gaskets and they were fixed yesterday along with scoping cylinders through injector holes all cylinders show perfect crosshatches for 180k on overhaul. So I'm hoping I see some improvement from exhaust being sealed up goodntight when I get back from cancun.

Previous work in last 6mo
6 injectors
Imap, Delta p, exh press
All 4 actuators
Fuel shutoff solenoid
Crank/cam sensors
Turbo and actuator 130k ago
15k oil changes rot 15/40
Mm tune
With cold weather idling uses about 1gal oil in 15k, about 1/2 gal or less when I don't have to idle.
Think that's it.

If there's anything else I should look at please let me know.