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

My only qualm about towing that fast up mountain grades is the transmission temp, not at all the engine. 4000-5000 rpm sounds horrible compared to what you're used to hearing, but it's not bad for the engine. But really I think you need to lower expectations from the 65-70 mph range, because slowing down while towing & climbing is not at all a bad thing for your transmission.

If the rev noise bothers you, just back off to 55 or 60. Or trade it in for something with a turbo die$el.