Some of the main highways in Canada are more like 11%. Some of the grades in the western US are 10 miles or more. A good test for any tow rig would the road to Death Valley coming from the southwest. Around ten percent grades and many thousands of feet up and down over several ranges. Even with a one ton truck it makes sense to pull over and cool down and rest the brakes.
I will never understand "just enough truck."
A one ton diesel gets just as good of mileage as a 1/2 ton gas truck, maybe better. Especially with some bolt on parts.