From a trip I made a few years ago from PA to Yellowstone and back
4443 miles, 318 gallons of diesel, average 13.97 mpg
Worst tank, 12.3 mpg (head wind in South Dakota).
Best tank, 16.9, but that was only half a tank with half of that spent driving 35-45 MPH in Yellowstone and the other half the downhill run to the East entrance of the park and into Cody WY.
Best all highway tank 15 mpg with a quartering tail wind across Indiana and Ohio.
I do still wonder if different state fuel blends also have something to do with mpg differences from one tank to the next.
In the highly unaerodynamic rigs we drive wind speed can easily explain 10 mpg one trip and 9.2 the next.
I'm with wallacep. REALLY happy diesel has dropped. I only hope it stays down.