DD15 bad fuel mileage

Specs:
2009 Cascadia
10sp
3.36 rears
506hp

I am at a loss. I'm averaging 5.2 - 5.4 mpg running 1000 mile round trip loads half empty and half at 10,000 pounds. No matter what I do or how fast / slow I drive it gets the same.

I ran 2 identical loads back to back. The first was 1,050 miles. Empty halfway and 38k the other half. Idled for 6 hours and the fuel mileage was 5.2.

The next load I went to the same place empty up and 38k back. This time I ran at 72mph and idled 10 hours. Fuel mileage was 5.6. It just doesn't make sense.

Air filter and fuel filters have been replaced. Turbo has been checked. Charge air has been checked. It's been put on a computer and injector duty cycles have been checked. I'm down to thinking the EGR might be going out.

It also has a vibration when it idles that comes and goes and every one in a while, if you're starting out from a red light and go 1/4 throttle, it'll fall on its face then pick up and go. I idled 8 hours last night and used almost an 1/8 of a tank. Seems like it doesn't have the power it should anyways.

The fuel mileage is hand calculated. I don't have a screen with it on the truck.

 

I fuel at our yard. Rarely do I fuel on the road but when I do its mostly at TA/petro.

Tires are Goodyear G362.

Is there a way to tell if the delta pressure sensor or venturi pipe has been replaced already?

 

I haven checked that. Most of my experience is working on cummins, volvo, and paccar engines and the old 60 series. I'm still learning the new detroits. I'm thinking it has to be something simple otherwise there would be check engine light or the truck would run so bad that you couldn't drive it

 

If I run slower my fuel mileage gets worse. It's .2 - .3 mpg higher running 72 than 70. I tried 68 and it was just drinking fuel. At 72 I'm just a hair over 1500rpm

 

I've had the truck for almost 3 months

Also the dpf was cleaned when I bought it. I've never had a regen light come on and I've tried multiple times to do a manual parked regen. I hold the button down and nothing ever happens.