Last trip, I noticed my 2012 F150 3.5 ecoboost started to heat up about 5 minutes into a hard climb. Slowed to 60mph and it went back to normal. So I'm looking at having the radiator hot tanked and ...
If you were running the A/C, the cooling fan was probably already on.
You did not mention if you had the HD Trailer Towing Option. If NOT, I would replace the radiator with the heavy duty one that came with that package. I should be <$300 from a dealer, plus labor.
Also, only included on the HD Trailer Towing Option. If you don't have it, now would be a great time to add it.