no powersteering at low rpm/ loud powersteering pump

[96bmw318ti]

I had taken my 99 yukon denali 4x4 to have it aligned and they told me it had a bad steering gearbox. I finally got around to taking the time to replace the gearbox and i didn't get the results i wanted. At first i hooked everything back up and filled the pump as far as i could and ran the wheels back and forth then i topped it back off, and repeated a few times. So i took it down the road on a test run and the first thing i noticed was that the reman gearbox was about as loose as the one that i took out, just minus the dirt and mud that was in the pitman arm shaft of the old one. Then when i got to the end of the long driveway i started turning around and thats when the problems started, the wheels would barely turn, then i get back down to where i was working on it, and checked the fluid levels. The fluid was fine, it just seemed to have a few air bubbles in it. My dad was in where i got the gearbox and when he told them what it was doing they gave him a bottle of powersteering repair and told him it sounded like it had a sticking valve. I put it in the pump and I can steer it to the left fine as long and the engine is at or above 2,000rpm but when i can steer it the pump also makes a nice whining sound even though it is full of fluid. I am stumped and all i have been able to learn from a few people i know is that it sounds to them like a bad steering gearbox. I would apreciate any ideas about what it is, or what i could test. I have never had to mess with this type of steering before all of my other vehicles are rack and pinion. Thanks for any help.

 

[chevync]

I can cut my wheel left or right at low rpm and it will "catch" and you can hear a little grunting from the power steering pump, mechanic told me it was a weak power steering pump, ive also been told it could be a filter in the power steering pump stopping up?