My steering locks up while driving when I turn.

You need to have this checked by a front end shop. Though it could be the lack of pressure, based on what you have changed it could be front end parts going bad like tie rods etc or I have had vehicles that the internals of the rack wear out. The one I had disintegrated internally and sent fragments throughout the power steering seizing the pump thus smoking the belt and extremely hard to steer. That was a lot going on in that few minutes. Again, get this checked at once by a front end shop