I have the truck you are considering except 2WD but with 3.73 axle. When towing on the flats the sweet spot of the engine and tranny is 62-65 mph. There is an awkward area below 62 where the torque converter is locked in OD and the engine lugs and fuel economy goes down. When in hills I travel in Tow Haul which locks out OD and reduces exhaust gas temperatures which have a tendency to spike. A little noisy but commendable performance.
I tow a 10k trailer which is fine behind the truck.. If you want the 4.10 axle to tow 15k trailer then maybe look at a next generation truck. This isn't based on experience just a gut feel
