It is about what you would expect: expensive.
We started the journey from Louisville, Kentucky to Belgrade, Montana relatively heavy, the back of the cab filled to the brim with ten day’s worth of provisions and gear for alpine camping. The bed filled with a spare tire, compressor, stocked fridge, extra fuel, MAXTRAX, some tools and two ActionPackers loaded to the hilt. After packing it all up, the truck weighed in at a little over 9,000 pounds, and we set off on the journey.
Setting in the cruise control at 75, we cruised across the Midwest and into the plains, wandering up to Omaha, Nebraska and setting northward to pass through South Dakota, northwestern Wyoming and finally almost the entirety of southern Montana. Using whatever the lowest octane blend of fuel there was for consistency, we got a return of 14.7 mpg for this stretch. Sections of highway that were posted at a 80mph limit were traveled at that speed, with the exception of a 120-mile stretch through South Dakota were a 20mph headwind necessitated slowing down to 70 mph to retain some semblance of fuel economy.
Upon our arrival in Belgrade, the truck was fitted with a hardshell rooftop tent, which adversely affected the fuel mileage by about one mile per gallon. As such, the average fuel economy, including our off-road time, which consumed an entire 31-gallon tank of fuel, averaged out to 14.1 mpg, a total consumption of about 295 gallons of fuel for the entire journey. With average fuel prices hovering around $2.80/gallon, that put us at a total cost of $826 in gasoline.
Worth considering, while a diesel may return slightly better fuel economy on a trip like this, it is important to point out that average diesel fuel cost on this trip ranged from 30 to 60 cents per gallon more—and in a few places over a dollar per gallon more—with a quarter of the stations visited not even stocking diesel fuel. It pays to play, regardless of your choice of fuel.