PLEASE help me! VNL670 with an ISX CM2350 4.4 MPG!

[VNL670]

Good evening everyone. I am an O/O in need of some serious help or advice. After totaling my 2007 VNL670 with a Cummins CM870, I bought a month ago a 2014 VNL670 (VIN:157174) with a 525 HP ISX CM2350 (ESN 79646948) and a manual 13 speed. It had a CIL when I bought it. I took it to the shop in Venus, TX and here is what has been done so far, but not on the same trip. Please keep in mind that the truck started to lose MPGs around 2 - 3 weeks ago.

1. Oil change, air & fuel filters. (complete PM)
2. Oil pan gasket
3. Upgrade fuel pump inner rods from ceramic to metal with a rebuilt head unit from Cummins.
4. Baked & cleaned both DOC and DPF filter.
5. New injector DEF doser and gasket.
6. All new DEF sensors. (All sensors have been changed except the ammonia sensor on SCR)
7. New Delta-P sensor.
8. New I-map sensor
9. Exhaust gas pressure sensor (Close to the thermostat).
10. Fuel rail pressure sensor.

The issue is that after all these repairs the truck is only getting around 4.5 mpg (at the pump) cruising at 68 mph at 1400 rpm with light loads (50000lb - 60000lb) all in the South and Midwest. Currently there are no CIL on the dash or any messages. Boost gets to 35-37 on the gauge between gears and shifting or up-hill. Doesn't over heat and does not run hot like my old CM870. I fill up the DEF tank every 4-5 fuel fill-ups or roughly 4000 mile (give or take). It drives fine but just using a LOT of fuel. Ask me anything you want and if you need pictures, let me know. Any advice on what else to replace is highly appreciated.