I know that in the payload they generally have a 150 person included on it... but the difference isn't a matter of another 150 pounds...
Payload does not include any allowance for a driver, it is simply the GVWR minus the curb weight. The "tow rating" is usually calculated with 150lbs for the driver but it is often confused for payload ratings.
As mentioned, the rating range you're seeing is likely what's found in brochures and is the high end for a base vehicle. Specific payloads will vary dependent on cab configuration and options. The number found on the door jamb is specific to your vehicle but even that will be reduced by aftermarket add ons like the bed cover. 1200-1600lbs is the normal range for 1/2 ton crewcab 4x4 configured trucks (without HD packages etc)