Your towing capacity depends on which transmission, rear end , and cab configuration you have. For example the 4.6 4x4 with the standard trans and reg cab with the 3.31 rear end is rated to tow 2500 lbs. Same configuration with the auto trans is rated to tow 5800 lbs. Supercabs tow 200 lbs less.
Take the 6250 lbs and subtract the weight of your empty truck to get your truck load capacity which includes people, luggage, and your pop up camper. My guess is something in the 1700 lb range. If you have a lower ratio 3.55 rear end it increases your tow capacity by 1000 lbs.