on flat ground for short hop's maybe but i wouldn't even think about it with mountains, you have a 2.5 engine pulling a lard ass car allready and when you say "The Xterra just didn't have the grunt for the mountain passes. " the 525 ain't going to do much better and may munch a tranny trying, sounds like time to score a cheep v8 tow vehicle like a old pick up or suburban