Overloaded or wrong truck?

I don't think your fitting 150 gallons of fresh water in a slide in camper. If you couldn't haul that camper on a 3500 DRW without it being over weight, what is your option, a 450-4500 only? I have to think either that truck wasn't right from the factory or they ran the Baja 1000 while they were in the area.