Sorry I have to call BS on this one!! Please don't take me wrong I am not saying you don't think you got almost 25 mpg, I am saying you didn't realy achieve this. Did you go off the readout on the overhead? If so you know a chip or program totally throws the reading off, don't you. There is a very popular member on another forum who has heavily modified a 2 wheel drive PSD, lowered, all the un needed weight removed, custom made 3:08 gears in the rear diff, and heavy aerodynamic mods, this thing is a shell and looks like a proto type of a space ship than a superduty truck!! He has been featured in many diesel mags for his achievements and to my knowledge he is right at 24 mpg, and if I do recall correctly it is the low 24's, so you see I how I have serious doubts that a stock PSD is going to blow his numbers away.
Glad you had a safe trip though.
NCH