Diesel truck - tuner / program?

[Jeffrey Lebowski]

Do you have 4.10 gears? That could explain the difference in mileage with your 2003 (assuming 3.73 rear end).

Yep, and I'm sure you're probably correct.

^ This.
Don't believe all the people saying they are getting 10000 mpg after a tuner and some small mods. Just isn't happening and they are victims of the common core math system.

Sort of what I'm learning more I read. I don't help my case on mileage at all, but I'm also just not looking for speed and power. I don't tow and I have a car.
I'll need to think on this more. I did a bunch of reading about this for my old truck, then haven't thought about it forever until now. Now I am again, but I think I'll have another expediture here soon that'll eat this "entertainment fundage."