i recently pulled my 7500lb trailer up to 9260' elevation. the truck pulled great, but i saw my tranny temp go to a solid 250 and maybe to 255 degrees. it was a long pull, ten or so miles up 7-8% grade. outside temp started at 90 at the bottom and ended up in the high sixties at the top. i pulled over at the 2/3 point when my temp reached the greatest to idle and cool a bit. i was a kinda freaked as i've never seen it get above 220. i was fully expecting the trans light to go off, but never saw it.

now i've read several threads and can't get a solid answer to the question and also there have been a lot of mixed comments that the atf is breaking down and there will be doomsday to my tranny if it is not flushed and changed right away, yada, yada......my temp gauge is "inline" to the tranny radiator, so it should be reflecting the hottest temp (correct?). does anybody have a rock solid answer to the threshold temp for the tranny light and the effects on the atf at this temp?

thanks in advance..............................