Andrew,
I assume that by saying "Running the 75 series over the 80 series" you were referring to the aspect ratio on the tire. If so and you are running 295/75/22.5 tires instead of 295/80/22.5 tires, and in doing so you have a tire with a lower weight rating, so you need to check your wheel loading and increase your air pressure to compensate for the lower capacity tire. On a Monterey this should not be a problem, but on heavier coaches like the Marquis, the 295/75/22.5 can be overloaded even at max inflation.
Gerald