Cheapest thing to do first: Get a Load/Pressure Chart for your tire size. The one from michelinrv.com works for other brands as long as size matches.
Weigh the coach at a truck stop. Adjust tire pressures according to the weight and the chart. Any E-series prior to 2008 chassis year should NOT carry more than 65-PSI in the front tires, since that's corresponds to the 4600-pound max for the front axle.
This'll cost $10 for the CAT scale at the truck stop. If you tow something, have it hitched up. You'll get weights for Steer, Drive, Trailer. Rig should be loaded (including passengers) like it will for an RV trip.
