newdude covers this spot on. Depends not just on Z71 trim, but wheel size, etc.
My RST Z71 with 20"s came with the Wrangler A/T. Most of the RSTs with 20"s I've seen on lots, however, have the Dueller. Who knows how GM decides which one gets which.
I'm already looking forward to replacing them with Michelin LTX M/S2's, to be honest. Can't beat that tire, and probably has just as good of "off road" performance as the Wrangler ATs does. At least for the amount of "off-roading" I do... which is next to none. Lol