Your mixing apples and oranges. That ones that have 3200 lbs of payload don't have 2800 lbs on the rear end, they have closer to 1800 lbs. Actually, in the current model year the heaviest one has 2153 lbs on the rear end and its a Raptor, not really your typical tow vehicle.
Your confused.
Never said any F150 rear axle weight was 2800 lbs. Reread what I said.
As I stated these trucks are weighing in the 2300-2400 lb range according to those owners who have weighed them.
Hell even Fleet Ford weight specs shows a F150 std cab 5.0 engine 141" wheel base 2wd has 3270 lb payload and a 1847 rear axle weight. Now add that 3270 lb payload in the bed = 5100 lbs.
The point is using those gvwr based yellow tire payload stickers on "some" (not all) truck can and has overloaded the trucks rear axle when its placed in the bed such as hitch weight or a truck camper or a load of RR ties from the local farm and ranch stores.