More power for my Ford E450 32 Foot Forest River Sunseeker

You probably just need to put your right foot down firmly. The V-10 is made to rev and lugging up the grades is the worst thing you can do to them. You should be able to climb any 6% grade at 55, it may take 4,400 rpm(max HP), but that is what they are designed to do. Yes your mileage will suffer but that is just what it costs.
:C