My camper is 13K dry, 14K loaded. I drug a utility with a pair of kayaks and some random camping crap behind that yet so i was probably 16,000 pounds total.
My truck is a 2015 cummins crew cab long box with 3.42 gears.
The trips i made with this rig were through some nasty rolling hills, I mean I'm in Nebraska so our hills aren't terribly long or anything

but several of the hills had truck passing lanes to give you some idea. Now on the flats I let the truck easily roll into overdrive but when we got into the hills i locked it into 5th. The only time the truck ever down shifted was going down hill to maintain speed.
I feel that 3.73 gears would make quite a difference and I'd even more so like the 4.10's while i am towing, however to see 20 mpg highway empty out of the 3.42 gears makes me content with the gear choice. I tow occasionally and i am empty more than i am loaded so the empty performance is more of a priority in my case.
I dont think you can go wrong with any choice you make. If i had the option or the finances to allow me to hand pick/order my truck I for sure would go with the aisin and 3.73 gears. As it was stated you end up with a higher HP/TQ rating as well as the better gears...
My dad runs a 2014 crew cab long box aisin tranny with the 3.73 but only nets about 16 highway empty... some of that mileage difference of course is going to be the extra contact patch of the tires but IMO more so the gears...
long story short, dont fret the details too much...