Who said anything about a mechanical defect? I do know that Ford's Unintelligent 4WD System doesn't work as most are lead to believe though.

I doubt if the tires are bald at 5100 miles. Over inflated? Not by me but I did get a oil change at the dealer last week, no telling what they did. I guess that you haven't heard about the hypermilers running 50psi and claiming that it affects nothing but increases MPG??

I will check the air pressure. You can find tons of stuff on problems caused by under inflated tires but nothing on over inflated tires.