If it won't return to center the fault could be in the box or in the geometry What came in the power steering kit?
Have you checked the linkages for binding? while the suspension is at ride height? Is there any exhaust rubbing?
You said the car had an FEA? Did you get a spec sheet when it was done?
Is the box centered properly? The wheels have to be in the straight ahead when the box is positioned on it's "hard spot" in the center of its rotation, otherwise your car will wander.
A faulty box can cause all of the problems you have, but you should check the rest of your front end. Was that box rebuilt? I have seen junkyard boxes not work right if they came from a car that took a hit to the front wheels, and forced the box past the stops. Also if someone tried to "adjust" a worn box to get the freeplay out, and it is TOO worn, they won't return to center properly and will be sticky in their operation.
Also a box that is not mounted right can get bound up. I saw a car that had a 605 box mounted on a vega mount. The stands were too short and flexed the case until it got sticky.
I would see if you can try another box to see if it is in the box.
Hope this helps, mikey
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