4WD would not work in higher elevation

I am going to assume that this is electronic shift and not manual as it wouldn't make sense if it were a manual shift.

With that being the case, I think this was just a coincidence that it failed at higher elevation and then started working again. The first reason, is just going up a bank is not going to be that much of a difference in elevation from where you first engaged it and it started working. So even though you went higher up a bank, unless the bank was hundreds of feet higher it wouldn't make any difference. The next reason is, you have an electronic shift motor and not a vacuum motor that could be effected by thinner air.

So that means we just need to figure out what is happening now that it is sluggish. I suspect this is the motor causing this issue. We need to test the relay just to make sure the actuator is getting the proper power as intermittent operation could be the relay.

Also, if you have not changed the fluid, I would go ahead and do that. Here are some videos that will help with that:

https://www.youtube.com/watch?v=Lp8fDuRJMAA

https://www.youtube.com/watch?v=jywt228y8UM

Let us know what questions you have. Thanks

Okay. I understand but you said that it was working when you were in the mountains to engage and climb an incline but then it didn't work again. Unless you engaged it and then drove up a 500 foot elevation and it didn't work at the top, I would think it is a coincidence.

Because it is electronic shift, I suspect the actuator is the issue.