if you read the sticker on the pillar once you open your driver side door it will say something like "maximum weight of cargo and passengers not to exceed 3628 lbs" and then list the 65lb fronttire 75lb reartire pressure. so if you have 3628 lbs in the truck then you should be at that recommended air pressure. if you have more then go up to 80lbs, if you have less weight in the truck let some air out. This information would only be accurate if you are still running the stock size tires & load index rating.
I travel with 80lbs of air in the rear tires and the recommended 65lbs in the front as my camper is heavier then what the truck says it can accept. I'm also not running the stock tires.
mfg rate the tires at cold pressure knowing they will increase in pressure when hot which is why the sidewall always states, inflate to 80lb psi max (cold)
happy camping