Well...............in the 80's I had an Eagle that got 12mpg and my Freightliner gets as much as 11.9mpg. Even though that is a true statement, an explanation would be proper. The Silver Eagle was a fluke. I had a buddy that had a brand new Eagle with a V892, and a 4 cylinder diesel generator. It got 1 to 4 mpg.
The first trip in the Freightliner I drove 70 mph and got 8.6 mpg. The next trip: the road was level, I went 65 mph, did a bit of drafting, and got 11.9. High numbers are possible if you work at it real hard.
On the last trip I was in a hurry and gave it the GK hammer......I purposefully didn't check the MPG.
Doc Weaver '98 Freightliner FL60 pseudo toy hauler