BLE… I wasn’t talking about the same hill as your answer suggests. Please don’t take it out of context. How fast you would have to travel to maintain the same average would depend upon the time traveled within that ten mile total distance which if the same as 50, would be 90 miles per hour. Please read the "or " part of the statement which was conveniently disregarded in addition to the phrase “if at any time”.
Your example is not scientific but if it works for you, so be it. I can average nearly 30 mpg in my 4Runner too if I keep the speed below 55 with slight grades as I have done. But guess what, I could do better with no grades at all. Bottom line; it’s still a low 20s mpg highway at 65 to 80 mph and traveling around at less then 55 on slight grades does not prove a thing when wind resistance at higher speeds, which in part, determine our EPA figures, are disregarded. EPA uses level ground.
It is my contention that a car(yours) does better than highway or average mpg due to lower non stop and go speeds, and not because of slight grades. Just google terrain and it’s effects on mileage. I don’t feel I’m alone.