The pressure on the side of a tire is the maximum pressure you can safely put in that tire. The only time you would want to use that is if you have the maximum recommended load on that tire.
My class A (right at it's 20,500 lbs GVWR)with similar tires requires 80 psi to carry the load per the tires load and pressure chart. I run them at 85.
I suspect you are carrying too much pressure and thus a harsher ride. However, until you weigh it, you can't be sure.
Mark
2000 Itasca Suncruiser 35U on a Ford chassis, 80,000 miles
2003 Ford Explorer toad with Ready Brake supplemental brakes,
Ready Brute tow bar, and Demco base plate.