1974 power wagon questions

Power wagons regardless of trans are all still 1:1 in high gear.

Also the stock no-power 318, and modified 360 get the same mileage.

My dad still has his 78 power wagon he bought new. 360 4-speed. 14.5 mpg
He was an accountant, so every gallon of gas was recorded in a log book.
From brand new until 240,000 miles it basically got the same mileage.
He quit driving it a few years ago, for a more modern truck.