Freightliner power steering problems

I have a '13 Cascadia and 3 days ago I was unable to turn my steering wheel to the left while stopped. I was able to turn to the right at a stop and also able to turn left or right while moving. Started with the easiest first, replaced p.s. filter and drained system and cleaned reservoir. Had truck jacked up to have front end parts checked which resulted in no problems found. Then replaced all 3 hoses thinking maybe there was a restriction, then removed the steering box and took it to a company that test and rebuild. They tested and said it was working as it should. Told me I would be wasting money rebuilding since it passed their test. They felt strongly that the pump was the problem. Purchased a pump the next day from Freightliner had it put on. Test drove and still the same problem. Cannot turn left at a stop but can turn right. I have to be able to turn before I start moving as I back into some yards that are a very tight squeeze and I have very small amounts of pull up room therfore I need to be able to turn before I begin moving.
Please help!! Any suggestions appreciated. I'm out over $900 with a problem that no one seems to be able to resolve.

 

I was told that they connected a p.s. pump to the box and and sent pressure to determine whether or not the piston inside the box was properly moving upward and downward. And they confirmed that it was.

 

Will try, thanks.