I'm clueless Rick, but since steering is not something to be without I would get on the horn to the Prevost experts, possibly at the engineering level. Since power steering pumps are merely gear pumps they either work or they don't, so I suspect you issue has to do with valving in the steering sector. Why it happens is the question.

FWIW, if you want a little help when the steering is not working lift the tag. It won't make the steering stop malfuncting (I made that word up, Lew) but it takes a little weight off the front end.