Yep, hence my quote on using a sun-dial.
I was flat towing a Jeep CJ-7 to the mountains to play for the weekend, with my 81 d-150 /6 833od, with a 4.56 rear gears.
I got passed by a semi-with trailer on a 2 lane mountain road.
I said to my wife, I needed to un-hook the jeep, and tow the truck up the mountain.