This may be a little late, but...
None of the xterra's are huge on power, thought the gen2 is about 80 hp more than the gen1. The 2012 has about 261 hp. It has a rated towing capacity of 5000 lbs, but if you're going up high altitude/steep mountain passes you may find that it's a little on the slow side. It will do it, but you're going to have to be patient and you may piss off some other drivers that get stuck behind you in stretches where the road drops to one lane.
Keep in mind that with altitude, vehicle hp and gas mileage tends to drop due to less oxygen.
Regardless of which vehicle you choose, do make sure that you have an auxiliary transmission cooler installed. It will greatly increase the life of both your transmission fluid and you transmission.