Just from my experience, I have had very few problems with power steering boxes, plus the fact that it seems like your problem has to do with engine rpm. You could always buy a high pressure pump and if that doesn't solve the problem take it back
![Confused :conf:](https://board.marlincrawler.com/Smileys/marlin/conf.gif)
. Though, I wouldn't advise doing this too often, parts houses kinda get irritated about this kinda stuff.