The root of the issue is simple. The cooling system is not operating efficiently. The h55 would generate less heat in 4th than the a440 transmission given the same hill, that much is a given.
I worked on a 60 a couple of years ago that had severe cooling system corrosion, and would overheat in all situations, even idling in the driveway. Investigation found that the coolant was so old all of the aluminum components effectively dissolved.
New thermo housing and thermostat, and water pump later, and the truck still had issues. I had the radiator hot tanked, and flushed the block with a mild muratic acid solution, and it was perfect after that.
I worked on a 60 a couple of years ago that had severe cooling system corrosion, and would overheat in all situations, even idling in the driveway. Investigation found that the coolant was so old all of the aluminum components effectively dissolved.
New thermo housing and thermostat, and water pump later, and the truck still had issues. I had the radiator hot tanked, and flushed the block with a mild muratic acid solution, and it was perfect after that.