I think the longest stretch in the area is now down to 82 miles. But the little stations come and go. I'd plan on 100miles and you'd be safe. We plan on 200 miles. Electric runs pumps, a storm means no gas.
We have never done less than 9mpg or over 10.5mpg on average in 13,000 miles.
We use torque and it gives me a very good display of percentage of fuel left and gallons per hour used.
We have TORN UP the area from Kanab Utah south to about Florence Arizona and all along the Arizona and California portion of i40.