I find this REALLY interesting! I was an automatic trans engineer at Ford from '88 to February of this year. The last three years I was a trans cooling engineer.
Are they in 4x4
high or low? Running at full load at 20 MPH in 4x4
high is going to cook the trans. There may not be a way around that. Keeping the transfer case in 4x4
low puts a 2.7:1 ratio in the driveline, which will reduce the load on the trans by about 2.7:1. At 20MPH in high the torque converter will be unlocked and making A LOT of heat. In low range the converter may be locked, I'm not certain. Even if it isn't locked the loads will be a lot lower, so it will create a lot less heat.
If you already are using 4x4L, regearing both differentials would help a lot.
Do you run synthetic ATF
? Getting dino ATF
to flow through an air to oil cooler at the ambients you see will be a problem. I've seen dino fluid gel in the cooler at about -20F, and I know you see a lot lower than that. When the fluid gels a bypass opens and then there is NO flow to the coolers. Your trans would have seconds to live after that happens.
Yet another problem you have is that if your 2000 model year trucks were built before February, 2000, they don't have a cooler in the radiator. You need that!
I think an air to oil cooler may not be the solution here because of the extreme ambient temps. A really good water to oil cooler may do a better job.
I did a quick search and found this, for example. I don't know this company, but this is the type of heat exhanger that I was thinking of.
The way to do this would be to mount it anywhere under the truck or under the hood that is convenient. Location is not important. Run the ATF
through it and use water returning from the heater to cool it. You don't want to use water directly out of the radiator because it could be too cool and cause gelling. Heater return water is plenty cool enough to keep the trans cool.