I've got a 1991 Suburban 4x4, 3/4 ton 6.2 with banks turbo, the pump rattles and is jumpy when you turn the wheel or push on the brakes (cause it's hydro brakes, obviously) I've tightened the belts, and checked/replaced the fluid. All lines were new about a year ago (no leaks) any ideas why this is happening? Its becoming scary to drive with the brakes acting up...does this sound like the pumps going out?

Thanks in advance.