I asked about this when I order my truck the bumper is rated as a Class III, I still order the frame mount Class IV, I don't need the wight but like the idea of the 2" receiver.
Maybe the 2013 is different and that's where the confusion is, but I don't think so.
The receiver hitch I linked to earlier in the thread is a 2" receiver and is not mounted to the bumper alone. At least in my 2011 and a 2012 that I looked at, there is a frame mounted hitch bar behind the bumper. The 2" receiver mounts to frame mounted cross bar with 2 bolts and then 1 additional bolt goes through the bumper center hole.
It's a custom fit class III receiver and only takes like 15 minutes to install. it's what I tow my camper with and is rated 600 lb tongue weight and 6000 lb trailer weight.
But with a weight distribution hitch like I use, it's rated 1000 lb tongue weight and 10,000 lb trailer weight - More than my truck is rated to pull.
Ray