bobbolotune,
Don't waste your time arguing with the dealer. Do your homework. Weigh the truck: fully loaded and unloaded. Determine the recommended pressures from the tire manufacturer's tables (for each axle) for fully loaded and for unloaded.
When loaded, inflate the tires accordingly. It's OK to run the truck unloaded occasionally at the "loaded" pressures. But don't run it loaded at the unloaded pressures.
Pay no attention to the pressures on the tire sidewall except as a do-not-exceed pressure. This is not the recommended pressure.