3/4 Ton or 1 Ton? Long Box or Short Box?

[Klondike]

I am purchasing a 2019 High Country 320MK with a hitch weight of 2,160 lbs and shipping weight of 11,085 lbs. Add in another 1,000 lbs of gear and the total weight of the 5th wheel will add up to about 12,085 lbs. I am now planning on purchasing the truck to haul it. I am looking at a 2016 to 2018 GMC 3/4 Ton or 1 Ton, Crew Cab 4X4. Both have a towing weight of between 13,700 and 14,000 lbs depending if it is a long box or a 6’6” std box. The payload of the 3/4 Ton is 2,943 lbs for the std box and 3,186 for the long box, and the 1 tons is 4,058 / 4,074 lbs.

So all trucks should be legal to tow the unit but what do you think is best? And is pulling with a long box smoother than a short box? I will purchase a sliding hitch so no worries there!