UORTC follows the I4WDTA methodology, perfected since the invention of the wheel by ancient Mesopotamians. No need to lock it unless necessary. With an 80 or Tundra with automatics, you can "lock" the differential with left foot driving. The differential follows the path of least resistance as designed, so a wheel in the air or with poor traction spins while the wheel with all the traction sits there. By applying the brake, you now in effect require torque to be sent to the wheel with the traction. In essence you lock it up but retain certain differential motion, and can control the amount of "lock" by how much brake you use.
If you follow me on the tough trails, you will see my brake lights never go off, even uphill. I get hard on the brake, select an engine rpm (say 1100), and keep it steady throttle. Then remove and apply brake pedal pressure to maintain and control the forward motion. It's magical.
I do use lockers on certain conditions, never while turning. Perhaps something to demo during our next ONSC event? Reach out to you local elected official....
Bill Burke is a Master Trainer for the association, and no one explains it better than him, around 2:30 into video