Txsurfer you need to pull out your owners manual and check it out. It should cover towing and maximum payloads and weights. Then once you understand that then you need to take just your truck with a full tank of fuel to a some scales. Usually you can find some CAT weight scales near a truck stop. Get your axle weights, and combined weight. Then you can compare your real numbers to what's in the owners manual and determine your maximum payload. You'll also want to look at your tires to be sure they align with the maximum payload too.
Hit up google for, how to determine my trucks payload capacity. Plenty to read and learn from.
