Gambler, I'm not saying your wrong, But I could not find an apples to apples comparison that would change the payload cap.
Yes, I do know that Ford does not make it very clear, and that there are a lot of variables.
That being said; let me gave an example.
Truck 'B' will weigh 300lbs more and have 300lbs less in Payload cap. than truck 'A'
Truck 'A' 10,000lb GVWR, 4,000lb Payload cap., 5,600lbs Tare (truck w/No passengers or fuel)
*That leaves only 400lbs left!
Truck 'B' 11,500lb GVWR, 3,700lb Payload cap., 6,000lbs Tare.
*That leaves 1,800lbs left!
It is all in the numbers and where you put your load!
For me, I would rather have the higher GVWR.