Just want to add something I did not see, and correct something else.
Tow/Haul mode by itself will not lock out AFM on the 2014-2018 Silverado/Sierra. If it does while towing that's only because the weight and wind resistance forces V8 mode. You have to put it in M and select a gear lower than your top gear. This also locks out OD. For a 6 speed, run 5th gear. For an 8 speed run 6 or 7.
I see people complaining about the towing ability of the 2014-2018 Silverado/Sierras on the truck forums. When asked most of the complainers have no idea how to use Tow/Haul mode or how to lock out OD.