Tires

I assume you are running our ST225/75R15 Load Range C Marathon tires now (rated to carry 2150 lbs at 50 psi) and are considering going to the same size tire in Load Range D (rated to carry 2540 at 65 psi). I hope you have 4 tires on this camper because with 2 tires, you are overloaded even with the LR-D tires. If all this is true, I think that new tires are a good idea considering the sidewall cracking on the old ones. I also think that moving up to the LR-D tires and 65 psi inflation pressure will help take some of the sway out of the camper.

I'm not exactly sure what you mean by "super size tires". Do you mean replacing duals with wide base single tires? Do you mean upsizing to 22.5" or 24.5" tires and wheels? Or, do you mean going to larger 19.5" tires and wheels? In any case, I think you should check with the vehicle manufacturer (in this case Ford and whoever built the ambulance package) to make sure that you have the proper clearence within the wheel wells, proper gearing and wheel bearing to handle whatever tire / wheel changes you want to do.

It would be best if you weighed each axle of your motorhome to determine the weight being carried by each wheel position. Then use the load/inflation tables found at the following URL http://www.goodyear.com/rv/tirecare/loadinflationtables.html to determine the pressures you should use. When in doubt, round up to the next highest pressure. A little too much air is better than too little.

I don't know what you mean by "all directions". I would suggest that you rotate the tires as shown in your owner's manual.