The bumper says 500 pounds tongue weight and 5000 pounds towing, could I actually tow that much off of the stock bumper, or is that a referance to something else?

 

Yes, it will tow that much. As long as it isn't rusted thru.

 

If you look at your owners manuel page 196, the answer is under Trailer frontal area considerations.
I interpet it to mean you can tow a utility trailer such as a flat top open type that does not present a lot for frontal air resistance. Then not on a regular basis.
Also see page 197 under step bumper use.
I would never tow an enclosed trailer of any large size and weight using the..bumper..and where you need safety chains and electric brakes, 7 pin connector etc that a step bumper normally dosn't have provisions for.
I admitt the book does not make all this very clear but you can now see why you would chose one over the other for safety.