The Mothership needs an MPG Boost

[brothermothership]

Thanks everyone for your responses, and just so we're clear, I did not spec these trucks....I am just trying to help the office through a bad deal they made. They obviously did not do their due diligence on speccing the trucks for their intended use and terrain, plus the weight of the freight they haul most of the time.
I have been making suggestions and adjustments, looking at the details to make the truck run better.

One update that did help was the progressive shift reprogramming, I picked up about .375 mpg just getting the transmission to shift earlier and faster. The rest of it comes down to engine tuning. Would a higher torque, straight rated engine program ( Cummins has straight 1750 ft/lbs and 1850 ft/lbs programs that would be a great base for some refined tuning that are in the 400 to 485 or so range, I think ) help with masking the transmission and final drive gearing mismatch? My thought is the added torque will help fill in the gap and make the truck more driveable in the mountains and cut the fuel useage in the flat/rolling terrain when driven properly. We can get the dealer to reprogram the ecm since there were a batch of misbuilds that came through and these trucks were part of them.