The Mothership needs an MPG Boost

[brothermothership]

Hey all, I am currently driving a 2016 Volvo 780 that pulls a flatbed at or near 80k most of the time. The combination is as follows: Cummins ISX15, Eaton Ultrashift + 10 speed overdrive ( .73 ), 3.36 gears, standard profile 22.5 tires, 450hp with 1550/1750 ST rating on the plate.
The vehicle has about 25000 miles on it, no trouble codes, and in general runs ok. The emission system is working fine. Despite all this, the fuel economy is not acceptable. I've tried driving slower ( 56 to 65 mph ), use the cruise as much as possible, and in general be kind to the Mothership. The best it's done is 6.5 with a load of straw from ND to TN that was tall enough to help with the aero and was 33k# ( about 67k gross ), but most of the time it's 6.0 to 6.3. I don't idle the truck much.

I did notice that the transmission programming was not optimized for best fuel economy, and the Eaton rep is coming out to put a low rpm/progressive shift program in the ecm to bring the revs down to 1500 or so rpms and to skip gears instead of running through all of them. The engine speed load breakpoint was lowered slightly to 1600 rpms. When it gets serviced again, I am considering going to a lighter oil like a 5W40 to reduce the drag. The trailer was out of alignment so it's getting replaced with a new Reitenour. I am also going to check the tractor alignment to make sure it's ok.

Are there any other things I should look at? How does the ISX respond to the lighter oils? Should I be concerned with cam and valvetrain wear? Thanks in advance for everyone's help.....there are 5 trucks similarly speced that are hanging in the balance.