I have a 06 f150 5.4 3v. It had a new crate motor with only about 10000 miles maybe less. I went to go camping the other day and was pulling a 4000lb camper and the truck overheated. The guage was all the way over to the red. I pulled over rite away and shut it off I got out and checked everything and everything seemed ok I started it back up and it was already down to where it always runs. I had my brother come get the camper and drove it all weekend and never had another problem. The next time it happened I was pulling a 18 ft car hauler and noticed the guage barely moved then just pegged out instantly same thing got out checked it all and started it back and it was back to normal already. I pulled a truck home on the car hauler not long before I pulled the camper but didn't have the ac on and it done
I put a new ac compressor, all new ac lines and it seems like since then is when it started but also didn't have ac before then. When I installed the motor I flushed the radiator with just water, put new water pump and a new thermostat. Only thing I see wrong is the condenser needs to be combed, dirty air filter, and needs oil change. Sorry for the long post just wanted to give all details so somebody can hopefully help me better. Any info would be greatly appreciated.