You just said it hit 230 in another thread... No one argues that fluid changes are important.
250F for an EXTREMELY BRIEF basis maybe, but
"Automatic transmission fluid (ATF) has a life of about 100,000 miles at 175oF. At high temperatures, it oxidizes, turns from red to brown and exhibits a burnt smell. In addition to reducing the oil’s lubricating quality, high temperature produces a varnish on internal parts interfering with the operation of the transmission. Above 250oF., rubber seals harden, leading to pressure loss and leaks. Also, the transmission can slip. In the worst cases,
clutches fail and costly repairs result.
ATF manufacturers suggest that for every 20oF. increase in operating temperature above 175oF., the life of the fluid
is cut in half. Hence at 195oF., oil life will be about 50,000 miles. Above 240oF., it becomes nil."
So you would want to change the fluid after any trip up in that heat range right away as the fluid is no longer good.
Yes. In the return line. A gauge would be nice, but I have my scangauge mounted and watch it every time I drive. Defintely watch for leaving some airflow room with the skidplating or you will bake the pan. With my skids we left plenty of ventilation to keep things cool.