Weight of the tires...

Note there is a Towing section of the forum with much more info, but no, payload cannot be increased.

 

If you have any factory installed options, such as running boards, you can remove them, and add their weight to the payload capacity IF their original weight was used in the calculation of the payload capacity. My payload capacity is 1661 lbs because of all the heavy options ordered from the factory.

I hear the bed side steps are heavy for the 6.5' box trucks, like over 70lbs for the pair.

You'll never exceed the factory rated max payload capacity for your truck as calculated before and options are added for each respective base model.

The yellow sticker in the door jam is custom for each truck based on options on the truck.