63 power steering problem

I just replaced the master control valve and hoses for the power steering on my 1963 Galaxie 500. It's a 390 tri-power. I've bled the system. There's circulation so I'm pretty sure that the pump is working. When the wheels are centered everything if fine. I rotate the wheel in each direction and things seem to be working fine. As I begin to put pressure on the system, ( the wheels actually begin to turn), I begin to hear a squeal. The harder I turn the wheel the louder the squeal. After a certain point, in either direction, the engine begins to lug. Does anyone have an idea of what I'm dealing with here? Any help would be much appreciated. Thanks, Thomas

Couple of things I'd look at. Lines connected to the wrong port on the pump. Lift the car so the front wheels are off the ground. With car not running, grab tire and try to get them to move side to side. Grab steering wheel and turn from one stop to the other. It shouldn't have much resistance but if it does then it could be a checkvalve or piston. If that is fine, start the car and try again with it off the ground. If the steering wheel doesn't turn it easily I'd be thinking an issue with the pump internally.