http://news.pickuptrucks.com/2014/07/more-game-playing-now-gm-fesses-up.html Not surprising. Ram will probably next. Or maybe not. Time for another standard for payload ratings.
I don't expect the payload listed on the website to be the real payload.
But when they say maximum payload I take that to mean the maximum. You know the highest possible payload available in any configuration from the manufacturer.
I do wonder what all they do delete to get their numbers. The door sticker on my truck is a couple hundred shy from what they put on their website and my truck is basic work truck trim crank windows and all.