I can’t seem to find my payload, all the door jam showed was the gvw at 6800lbs.
On that same sticker is the GAWR which should be 3900 front and rear, those are the ones you really don't want to exceed.
Payload is the difference between the GVWR minus the actual weight of the truck(trailer not hitched).
Goosenecks and fivers are usually more "tongue heavy" than a tag along counterpart with no way good way to adjust the front to rear axle (truck) loading. You also have to contend with clearance to the back of the cab issues, being a 5.7' bed you have even less clearance.
I can't remember which bed the person had, but there was another thread a while back about someone putting a gooseneck hitch in for transporting empty trailers around. The payload police all said no then too without taking in any actual weights.