Ok - this is JUST a short 35 minute highway run today where I found a nice tractor trailer I drafted (at a safe distance - but JUST inside the messy air where it smooths out), then 10 minutes in traffic till I stopped and took the picture - needless to say, Drafting can work WONDERS.
Bondo, Big Dave and the guys are correct - MPG on a truck are pretty much Aero.
35 minutes highway, 95 km/h (60 mph), drafting a tractor trailer.
***On a side note I do have a scangauge II running but by my hand calculations from the past 5 tanks - my onboard OEM fuel computer has been near bang on (ex.: last calc was 18.32 mpg average and the computer read 18.3) - so for running about, I do trust the onboard for now until I figure my scangauge out properly.