I averaged 17.4 MPG on my way home from Colorado.
I must be doing pretty good... That drive is far from flat... far from it... plus it's windy in all directions, sometimes it's a head wind sometimes it's a cross wind... etc.
I'm still running on the same tank from Rawlins To Ogden (that's 283 miles) And I think my trip o meter is at ~300 (at the dealer or I'd check exact) And I had a quarter tank (on the indicator) left.
We'll see where I end up...