I should make clear - this truck came new with 17" tires, LT, LR "E". They were Goodrich AT's. After 70,000 miles it was time, so switched to Michelin Defender LTX. From scouring the net, these seemed to be well liked by RV'ers and seemed to be better for the ice/snow daily driving Minnesota can throw at one. Of course, 3 months after purchase, I begin to hear that they aren't the best for sidewall stiffness. Load inflation tables for these don't seem to exist. In talking to Michelin, and the help person looking things up, very similar tires from them seem to recommend going about 10 psi above door sticker for the load I will be carrying. So, from 55F/60R to 65F/70R. Max is 80, so still within the margins.
I do have airbags leftover from when I had a fifth. But there are no plans to add them to the mix, so will just continue to air up to the 5lb minimum noted by Firestone.
The order of battle, when I get the TT from the dealer, will be: Make sure tire pressure is at sticker when I leave home. After picking up trailer, stop at the nearby scale and get weights. Air up all tires 10 lb above whatever they read at the truck stop. See what happens on the 60 mi ride home. If possible, check hitch tracking while on the way.