OP, there's a thread every week on the 6.2.
Haven't seen any real high mile reports on them but the 2 I've had for work trucks, a 13 and now a 15 have been good on the 40k mi or so.
No they won't get good mileage towing, no gasser does. Yes you will be running 4-5k rpms towing up most any hill and every hill at altitude, but they will get you from point a to b with a decent size trailer without issue.
I've only had 3.73s in mine and only occasionally tow 10-14k construction trailers. If it was my personal vehicle I'd get the deepest fears I could. 3.73s will hum along at a little over 2k rpms at freeway speeds. Too low IMO for a truck that makes its torque up high.