The manual and the pillar payload ratings are always different, with the pillar being the lower number. I have never been able to get a concrete answer on this.
The reason the payload ratings differ from the manual vrs. the door pillar is because each truck even if its is the same model may/will have different options.
Each option added reduces you payload by that amount.
There can easily be a 4 or 500 lbs difference in payload for the same model of truck.
The # in the manual for the base truck, add nav, stereo, different tires, different running boards, hitch etc, your payload drops.
Odds are, that your real payload is less than the door pillar #. How much stuff do you carry in your truck? that decreases payload. Most comapanies figure payload with a 150lb driver, if you weigh more, that takes away from payload.
The only way to be sure of a given trucks actual payload is to weigh the truck as you would normally drive it, then subtract that # from your GVWR.
Most people would probably be shocked at how small their real payload is, often 1/3 less than the manual states.