Exactly. The reason you are told to turn it off is the truck will go into OD when you let off the gas, then when you get back on the gas the torque converter will unlock, then it'll shift back to 4th, etc over and over. If you can monitor how your driving and temps, you can get it into 5th, the torque converter lock and you're good to go. If you just want to drive and not worry as much, just lock it out and let the torque converter lock in 4th.