Several years ago, my company truck was a 2002 F450 with the 225/19.5 tires. The tires had a sidewall max pressure rating of 110 psi, and the door sticker from Ford had a max psi of 75 at all 4 corners. The dual rear was a Dana 80 and was rated at 11,000 lbs with the 225/19.5 tires at 75 psi. No need to go higher than 75 psi as that was all the pressure needed to handle 11,000 lbs. I was only running the truck at about 9000 lbs on the rear axle, so I was still over pressure for the load but it was not recommended to run lower than 75 psi on the 19.5's.
I did the same on my dually with my camper, 65 psi in the dual rears which was rated up to 9350 lbs at that pressure. Never had a squishy sidewall or tires rubbing either.
Rich
