What is the Size and Load Range of the new tires? RV's used to come with "D" tires, and their max capacity was at 65-PSI. That sounds like what it would have shipped with. It is almost impossible to get new, Class C Sized LT225/75R16 tires that are not Load Range "E" which means you can go to 80-PSI and the TIRES will carry extra load over "D" tires.
There were cases where somebody, post Chassis Manufacturer, upped the ratings. I at least hope there was some reinforcement to go along with that. The only ones I heard of, were GM chassis that were branded "Workhorse" but maybe it was also done with some Fords. Workhorse assumed the warranty liability for the upgraded capacity.
Does the Coach sit Level? Easiest place to tell would be measurements from the bottom edges of the outside walls, down to the pavement. I'm interested in knowing if it's sagging to the front or the rear.