i have a 1989 gmc r3500 with a 454 that when its below 1000 rpms the power steering doesn't work but as soon as you rev it it works.its hydro boost if that helps any.the pump also runs the brakes and as far as i can tell they work fine.should i replace the pump or hydraulic brake booster or look elsewhere/would a bad brake booster block fluid to the steering gear?sorry if this is the wrong place