while using auto 4x4 the 2006 lincoln navigator quit running while I was driving

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first time I had any problems with my 2006 lincoln navigator, battery doesn't seem to be dead, I can try to get it started again but then it just dies, and it has plenty of gas. I was on my way home driving about 40mph and then it started to slow down so I thought maybe my 4x4 was acting up or something so I switched it off but it didn't help so tried to get over to the side of the road as much as I can and while doing that I don't know if at that point the vehicle had already died on me because the steering wheel was hard to move. I put it in park turned it off and tried to start it again and it would act like it wanted to start but then it would just die down again.