this s a question i don't see often. at what point do you realize before a trans breaks that you need to go ahead and get a new one?

i was doing some tuning yesterday on a truck and the shifts took forever to go through. i tried the usual changes to the tune but none would work. before he cam in the navy he used the truck as a work truck on the farm. he has towed a bull behind it and two horses and every other week he had a ton of feed in the bed. so i'm sure the trans has been tortured a few times. it was 77* yesterday and the trans was running around 175*. is this ok?