In the late 60s I had a '49 3100 with a '58 235. It had a 3 speed column shift and 4.11 gears. It was fairly comfortable up to about 55mph. At 60-65 the engine started making noise in the valve train and not fun to drive there. I traded it in on a new 1970 Blazer. I still have the Blazer.
I got my present '53 in 1976 and built a 270 GMC for it. It also had 4.11s in it with a truck 4 speed. Because of the mods to the engine and the cam I used it likes to run a 3,000 rpm. so 60-65 was in it's comfort range.
I put a Saginaw 4 speed in it and the Dana 44 with 3.55 gears. The comfort range went up to 65-70 mph. Now it has a T-5. With 29" tires 3000 rpm is 90 mph. It will cruse all day at 2,200 rpm at about 70-75 and 80 is not hard on it. I drive it hard and it's still used as a truck. A few years ago I made a 4,000 mile round trip from here to Austin, Texas via Ventura, California in one week. No problems at all except for water in the cab from some really wet Texas storms. You don't notice that much in Nevada.
There was an Over Drive unit made by Truckstill (I think) that fit into the closed driveline. I have only seen one and have been following that pickup for years. At some point I'm sure a younger family member will stick a V8 with an auto trans in it.
