After much time and grinding gears I figured out the 5 speed shift pattern!! And it sucks! Ha ha I need more on the top end! Ha!
Heck I don’t even use second gear right now! Ha ha crazy stuff. Must have really needed the low gears for heavy loads
Is it synchronized ? Try shifting at lower RPM's than your ears tell you to, old motors and old trannys like low rpms.
Old trucks were work trucks. They were used for many kinds of work. Its entirely possible that 1st was because a very slow truck speed was required for some reason. Might not have anything to do with grear reduction for pulling a load.