I don't know Chevies, but isn't the switch on 2010 and newer Chevies a tow/haul mode, as opposed to an overdrive lockout.
The difference is that it provides engine braking and changes the shift points, rather than just preventing the vehicle from hitting the upper gears.
I use it all the time in heavy traffic even when not towing so I don't have to slam on the brakes, but decelerate while on the highway.