Power steering problem

[larryboy_3t5]

I have a 70 Jimmy 4x4 with factory power steering. Put on a new pump and now when you start the engine it pulls violently to the left till it hits the stop. It will pull the steering wheel right out of your hands if you're not holding on tight. It stops when I remove the return line. Pump manufacturer says I have air in the system and advised to attach a vacuum pump to the reservoir and pull about 20psi of vacuum while working the wheel back and forth with the engine off. Did this till my arms fell off but the issue persists. Now they say it is a stuck valve or other problem with the steering box.

Anyone else run across this? I feel like the guy is just avoiding the issue of selling me a bad part but I've never seen this issue with power steering in the 40 or so years I've been working on GM cars and trucks.