Was talking to a buddy who has a 2006 5.9 and he said he was getting 41 mpg (Imperial)!!! I asked him how and he mentioned he had a "fuel mileage chip". He is talking 1200 km per tank without running it dry...

I will be looking into this one a lot closer when I get home (in Toronto until Friday night) and see this magic chip.

Will keep you informed about what I learn, be it bonus or bullchips!