Now I will say right off the bat I haven't owned my F350 long but these few things helped me with fuel economy.
#1. I quit driving it like it was a gas burner. Let the engine build. If you try to make this engine keep up with all the other vehicles then the milage will stink. Give it pedal and let it get there. Light foot goes a long way. Its hard to remember that we are moving a lot more weight than others around us because it will move it so easy.
#2. Turbo. Its kind of like a mother in law. Keep her out of it. If the turbo gets involved then a lot more resources get used.