Well, towed my first decent trailer today...trailer weighs 2,400#s empty, had a good cord of wood on it (figure at least 4,000 pounds, maybe pushing 5,000?); so around 6,400#s at a minimum. All this was using tow/haul and auto "D" (not manual)...2012, 2500HD, 4wd, CrewCab/std bed, 6.0L, 3.73s. I bought the trailer new, so its not abused. The chassis handled it excellent...no complaints there, felt just like my 2500 Dodge did. Handled the weight well. Powertrain, it was what I expected. It struggled on the little narrow windy/hilly back roads because you had no momentum to keep moving, you were basically trucking dead weight. Once on the bigger roads, it did alright getting and holding 4th, with some dropping to 3rd on the hills; and once on the interstate, it did fine even getting into 6th once you were on the flats (using cruise even). I would say towing at the max GCVW (9,400#s by my book) it would be struggling in this area (read: my home location)...on the interstate it would likely be fine in most cases (although I personally wouldn't tow heavy in the mountains with this setup after today's experience). Keep in mind, I'm trying to give this truck a fair shake. It did the job, it will definitely work for my purposes; I knew going into this it would be a whole different experience since I just came from owning Cummins for the past ten plus years. If I find I need more towing power, I'll do a gear swap to 4.10s or steeper. I do like the truck overall. The trans...I like it, but it takes some getting used to...its cool how well it holds gears both up and down, but when it drops into a lower gear and starts singing; it won't just shift up when you leave out of it slightly...I'd rather pull slower at a lower RPM than slower at a screaming RPM. Maybe its just me...just not used to hearing a V8 screaming at 5000+rpm.