Just wanted to add that the 2015 HD payload trucks will be quite different from the 2011-2014 HD Payloads that the OP is talking about.
With the 5L V8 or 3.5L EcoB, they keep the 4800# rGAWR, but now have six lug wheels; but they are special wheels that only come with the HD Option. According to the catalog, the 18" alloy wheels can carry more than the 17" steel wheels.
Because the 2015s with HD payload have the same rGAWR as before, but lower curb weight with the Al body, there should be more weight carrying ability on the rear axle. And the payloads are also higher than before.
To confuse matters further, the 2.7L EcoB has its own Payload option package that also boosts its payload, but not to the extent of the HD Payload package.
