My 2012 Silverado 2500 has all of that, it comes with the Z85 package I believe. Supposedly its electronic and if it senses sway it applies braking to both truck and trailer. I believe there is a video on "YouTube". I'll try to find it.
I have a Reese Friction sway devise, I still use it on long trips, have not noticed the GM sway control activate yet.
One feature I really like that is part of the towing system is the "Hill Hold" feature.
I have noticed this a few times, if we are at a light on a hill the brakes stay on until you give it throttle. There is an icon that flashes on the dash when this happens, I believe its the Traction Control system light indicating it is activated.