I was a bit surprised to find that my manual says to use tow/haul only when towing in hilly terrain. As a matter of practice, I use t/h pretty much whenever I tow. I will try the lockout thing as an experiment on the next camping trip.
2011 XLT, 4x4, SCREW, 3.5l Ecoboost, 6.5" bed, Max Tow, 3.73ls, camera, Rhino liner, Husky floor mats & splash guards, vent visors, Extang solid fold, Firestone Ride-Rite airbags, Sterling Gray Metallic. Towing a Jayco 23B hybrid.