2006 Explorer 4.6 v8 has no power to tow up mountains?

Agree with others, you are driving it wrong. I've never been afraid of RPM's and personally I like to hear the V8 sing. I've got the 2 valve version of your engine mated to a 5 speed auto/3.73's and it is more than adequate to move 5,000 lbs. of camper.

You don't mention what gears you have, but the tow package trucks were rated to > 7,000 lbs.