thanks slowmover.
i think the key to my success thus far is my 45 MPH/1400RPM average cruise speeds.
i also have a very light and constant foot.
about the only time i work this diesel engine is on the hills.i don't mind revving her up to 3k+ when loaded,where required.
other than that,i drive all the time like theirs an egg under my peddle and as if iv got no brakes.
i drive so slow and easy,id put granny to sleep.
i recently fixed a DRW problem,that i put off for far too long,and i'll be seeing great improvement from that (see my last two tank results.)
i also started with the lower sitting f250 hd 4x4 and converted that into a dually,rather than the higher sitting f350 drw 4x4 which likely helps some.