Fuel mileage still sucks

[Lead_sled]

I’ll try to give as much info as I can.

2009 Kenworth T660 Midroof
CM871
11R22.5 tires, virgen rubber on drives
Rear gears around 3.70’s
Overhauled by Kenworth dealership approx 400k ago
Everything in tact, nothing de-mandated. DPF replaced approx 70k ago
Drive down in south Texas. Mostly flat terrain and small hills

I’ve mixed driving habits to test. Drove aggressive and very conservative with similar results. I’ve read the suggestions of driving by horsepower vs boost. Higher rpms vs lower rpms.

When I disconnected the exhaust pipe to put the rubber plug to pressure test, I didn’t see anything abnormal that would indicate the doser leaking.

I plan on de-mandating the dpf filter and associated components within the next few weeks with the mm programming.

When driving on the interstate, I drive at 67 mph / 1450 rpm. I shift around 1800 rpm.

Everything else on the truck is in great condition. In fact, I got stopped recently for a level 1 inspection. I’ve got one of those pretty orange stickers on my windshield.

Everything is all original. Only thing that my uncle mentioned to me before selling the truck to me was that he brought it to the dealership and had it turned up to 525hp.