My 91 ford econoline work van has a 5.0 engine. I can drive it all day around town and on highway never runs hot but when I start home up the mountain it starts running hot, can anyone help?

It may be additional heat generated by the transmission; therefore, consider installing a supplemental transmission cooler. Another strong possibility is corrosion and mineral buildup inside the radiator, which is apparent when you go up mountains. The only solution, here, would be to replace the radiator. If you haven't done so recently, consider changing the transmission fluid and filter.

My 91 ford econoline work van has a 5.0 engine. I can drive it all day around town and on highway never runs hot but when I start home up the mountain it starts running hot, can anyone help?
I would try a radiator flush and change the thermostat