I've got a '14 2500 6.4L with the 3.73s. Towing a '15 Boundary Waters 301BH, about 6400lbs dry, somewhere around 7K loaded.
I do most of my towing around the Black Hills area, 3000-5000 feet of elevation, with some decent but not monster grades.
It does the job well for the weight of my camper. I've never had a problem maintaining speed or accelerating, even on a climb. Never needed more power than what I have. It does sometimes drop a couple of gears, so I often climb hills at 3500-4000rpm, higher than a diesel would need to. But that doesn't last long, and doesn't bother me.
I've gotten anywhere from about 8.5 to 10.5 towing, depending on terrain and wind. Lots of variation of both here. 9.0-9.5 is most common. 16.5-19 unloaded on the highway, mostly dependent on speed. Around 19 at 60mph, 16.5 at our new 80mph speed limit out here.
No regrets here. I've had a Cummins in the past, but it was overkill for what I need now. The 6.4L does the job comfortably, and considering my camping trips are close to home, and add up to fewer than 2000 miles a year, it's far more cost effective than the Cummins.
I'd buy the same truck again.
