Thank goodness the GM hubs are full time locked. The vacuum and electronic locking hubs from Ford and Chrysler were often problematic!A long long long time ago, we had to get out and lock hubs to use 4WD.
Then came along automatic hubs, but you still had to lock them for full time 4WD.
Sometimes they'd get stuck in the locked position and we'd have to drive backwards for a few feet to be able to unlock them. In bad cases, we had to jack up the wheels to release the tension to be able to unlock them.
The AWD systems (on our Explorer) are good for my wife, so she doesn't need to think about it.