Hard power steering

I replaced the steering gearbox in my daughters 96 Cherokee and now the power steering doesn't work at all. It was very easy to turn the steering wheel with her old gearbox, now it's very hard. So I replaced the pump. No help. So I got a new gearbox and tried it. No change. So I put the old gearbox back in and it is hard to turn. WTF?! We bleed the system with the car jacked up, engine running turning the wheel like 50 times. I'm at a complete loss. Any ideas? The steering box and pump came from Oreiliys. We got a pump from NAPA but the bolt used to install the pully wouldn't screw into the pump so we returned it. The O'Riellys pump was exactly the same as the one from NAPA but the screw worked.