I think i can help you with this.
Auto lock on these trucks has been problematic since their inception.
Most people throw away the factory Vacuum hub locks And instal a set of Warn hubs. Much more reliable, but you loose the auto feature. I’ve done it on several trucks over the years. The vacuum lines just get blocked off with RTV or a ball bearing etc.
Same as another poster above, come winter where I am, you lock the hubs and then select 4 wheel drive from the cab when you want it. Typically, in any truck I have, come sometime in November up here you just put it in 4 wheel drive and leave it there till April.
Just don’t leave it in 4 wheel drive on bare dry pavement. Hard on it. The tires all turn at slightly different rates, slippage, tire wear, and particularly if you are turning. The out side wheel has to turn much further. If it is in 4x4 the inside wheel has to be able to slip, as in on snow or ice. Or, something has to give, such as an axel.
The Ford electronic shift on the fly is basically the same function as the stick shift, just does it differently. It allows you to engage The transfer case when moving up to a certain speed. All it is doing is engaging the transfer case to the front drive line to the wheel hubs. The hub locks lock the hubs to the front axl drive. If they are not locked, it is just turning freely in the front hub. Conversely if the hubs are locked and the transfer case is disengaged (2x4) all that is happening is the front hubs are locked to the front axles actually driving the driveline to the transfer case. Harder on fuel because it has all the extra weight to turn. But not really hurting anything. Just more wear and tear.
The factory vacuum lines leak, break, get blocked, etc etc. You can be for ever repairing them in my experience. And the seal on the selector cap it self gets full of dust, dirt and salt, drys out, and gets very difficult to turn by hand. Another reason people do away with them. Warn are much much better. I’ve taken the factory ones apart a few times years ago and cleaned them up, greased them and put them back on, just to have the selector seizing back up in a year.
Other manufactures do it differently depending on the year, some were always locked, some locked in the differentials, some... etc etc etc.
I suspect someone has already changed out the hubs with after market ones.
On a lighter note...
Remember this, 2 wheel drive to get you in trouble... 4 wheel drive to get you out!