I test drove two 2011 F150 Crew cab 5.5' bed 4WD Lariats both with max trailer towing package. 1750-1850 pounds of payload per the driver's door. The Max trailer tow package offers a little higher payload for the 5.5' bed over 6.5' bed. But there is the HD payload package only available on 6.5' bed trucks which bumps up to about 2100 pounds of payload for very well equipped crew cab 4WD F-150s. You'll probably have to custom order a truck with either packages.
Ford bumps GVWR on 4WD trucks, so payloads are similar for the same equipment.