The tire manufacturer has no idea what those tires are going on. The best he can do is to label for maximum safe pressure.
As suggested do some homework and find a tire inflation chart.
Different loads will require different pressures. Fronts usually do not get adjusted that much as their load is more uniform. Rears you would optimally add more pressure as you increase the load and reduce with no load.
The pressure on the door is a "one size fits all" compromise that we all know is less than ideal.
Tire pressure is recorded at ambient "cold" temperature.
The questions you are asking seem awfully basic for a guy that owns a truck this heavy. I suggest that you read everything you can get your hands on regarding loading, weights, and towing.
