The listing on the tire refers solely to the tire's maximum capacity, which can very well exceed the truck's maximum capacity

The listing on the truck is a determination by the vehicle manufacturer of the proper pressure to safely carry the rated load of the truck while allowing for proper wear of the tire.

Too little pressure wears the outsides of the tread, too much wears the center of the tread. Both decrease traction.

More air increases the tires ability to carry a load, less air decreases it. However, pumping up the pressure doesn't allow the truck to carry more load.

They say there are no such thing as a stupid question.
They say there is always the exception that proves the rule.
Don't be the exception.