Interesting fuel economy day. We started out in La Grande, OR and drove to Snowville, UT. It is almost exactly 400 miles with speed limits varying from 65 to 80. I drove the speed limit as indicated. It is 80 from the west to the southeast of Idaho except in the Boise area and construction zones.
As an interesting sidelight, the low fuel warning light illuminated just as we hit the exit ramp at Snowville, so this tank is a good example of how much is left when the low fuel light comes on. The truck took 27 gallons on the nose at Snowville which means there should be 6 gallons of fuel left in the tank when the light comes on.......assuming the truck has a 33 gal tank, which I think is correct.
That tank, with quite a bit of driving in the mountains/hills, and 70 - 80 mph most of the time, netted 14.9 MPG hand calc'd.
Now when I fill the tank, I do it much like the TFL guys do it....I fill it until it clicks, wait 30 seconds or so, and squeeze it again until it clicks. I do this at least twice. I filled it that way in Showville.
We pulled in for the night in south Provo and I filled the truck to be ready for morning. I filled it the same as always except this time after I clicked it the second time, I let it dribble in to ensure a very full tank. The driving for this fillup was straight onto the highway at Snowville, up the pass, and then down into the Salt Lake Valley. From the top of the pass out of Snowvill it was mostly a gentle down slope or level at 70 mph. After filling this tank the same way I always do, I got an astounding 18.6 mpg.
At first I thought I might have short filled it some way, but after thinking about it I did not.....it was full. The only explanation is the gentle downhill and mostly steady, very lightly loaded 70 mph through SLC. Traffic was moving steadily and without stop. IT was an unusual day for traffic in SLC.
in no way do I think this tank will be representative of what this truck will do normally, but it is an indication of what it might be capable of if you need to extend your range, the topography is right, and you slow down.
All in all, it was a very interesting day in learning how this truck does on the road.