Hopefully a hydraulic engineer with some knowledge of RV hydraulics will post and can describe if there is some type of pressure regulator that can be adjusted or replaced. I'll just throw out some things in the meantime.
Out of curiosity, what brand of filter are you using. Is there an OEM filter available and have you tried one. The reason I ask is that some spin on filters have a built in bypass. Possibly, a cheaper quality filter may not.
What is that pump supplying, power steering, side radiator fan??? Do you have any issues with those?
Lastly, if there are no solutions, I would replace the hydraulic pump with a new or rebuilt model.
Hopefully you're not giving up on RVing and will buy another, maybe newer.
