Fuel mileage

[DDlighttruck]

2003 CM870 in a 2005 9900i. 3.70 gears, 13 speed. I try to keep it around 60-64 mph, and in the 14-1600 range for rpm. Hand calculated, I'm showing an average of 5.95 MPG for the last 20,000 miles. One tank that had to be a mistake showed hitting 7.4, the worst was 4.8. It's been as low as 3 mpg in the winter

When the ECM was "looked at", I was asked if I wanted power or fuel economy. Foolishly I asked for power. I was off road a lot, all flatbed and stepdeck work. Now I'm running a lot more highway miles and realize I made a mistake.

So is that my first step is having a fuel economy "setting" done to the ECM?

I've gone through the excessive fuel consumption tree on Quickserve, and I think I've pretty much got it done. Overheads been done recently, low-pro tires now, exhaust is tight and no obvious leaks, CACs been done (although hasn't been tested in awhile), EGR tune-up was done (150,000 miles ago), de-mandate at the same time the ECM was "looked at" (by one of the guys recommended on here), no check engine lights, I keep up on the maintenance of the filters and fluids. New CAC boots recently too, and new clamps.

Pretty much the last three to check are for any leaky injectors, fuel pressure and fuel restriction. Well, I should have someone more knowledgeable check my turbo, actuator, and actuator controller. Probably pressure test the turbo and CAC too

Is this about the best I can get from driving a brick down the highway?