OEM works better than the aftermarket stuff I've used previously.... its been my experience that you set it and forget it. no issues on my 14 and 16 year model pickups using the OEM trailer brake setup.
a cooler thermostat is not going to make much difference with on the road temps in the summer time with the a/c going..etc (towing). The truck is going to run hotter than 180F anyway. In the winter it might make some difference given the mod to the on/off on the electric fans. Not much gained on modern engine by changing the thermostat to a cooler settting...etc. You would be better served in my view to go with a larger capacity radiator if one was offered for your specific model truck. (Stock engine)
Once you exceed the temp of the cooler thermostat...thats it and you are dependeant on the fans and radiator at that point and its going to be very common to be over 180F towing or driving on the road in teh summer with the a/c on. The lower rated thermostat has not positive benefit at that point. In general the a/c will add 10 degrees F to the operating temp of the engine.
In the winter the truck most likely will run cooler, but it might screw with your fuel milage too...
2014 2500 HD, 4.10, 2wd, stock, 6.0 gas, long bed / reg cab.
I tow approx 10K (twin axle metal deck utilitiy style trailer / car hauler) trailer weights 3K, truck I tow weighs appx 6k...plus misc gear.
around 9 flat ground....worse in the hills, I generally run 70-75 on the hwy.