Excursion overheats&leaks tranny fl towing going 50,uphill

Has trans fluid been replaced?

Is it bright red, or dark red leading to brown?

Is there fluid on top of the trans by the vent, or only dripping off the bottom.

On the trans side of the issue, I would lead to foaming, which means it lost both it's ability to cool and properly function... which leads to more heat. Some Ford transmissions require an anti foaming additive which can lose it's effectiveness over time.