I am towing a Jayco 23J with my 6 cylinder 2011 pathfinder. I use a decent weight dist. Hitch and sway bars. I keep the trailer weight (fully loaded) at 4900 lbs. the trailer handles surprising well in terms of sway. Took a 2500 mile trip over 2 weeks last summer and was pleased by the handling. Power is a different story. Basically kept my speed at 50 mph.
We travelled to the Black Hills of SD and with elevations over 5000 feet, there are some decent climbs. Speed dropped to 35-40 in second gear on a couple of the longer climbs. RPM about 3500-4000 during same climbs.. Duration of those climbs was about 10 minutes but felt longer. As long as I took my time it was fine, just can't be In a hurry.
Something to watch is tongue weight. I'm really pushing the limit on that. I used air bags in the rear suspension of the Pathy to firm up the rear end. I also have the transmission cooler which helps.
All in all it's manageable, but I do not believe I could safely tow in the Rockies without cooking the trany.
Hope this info is useful.
Phil