You might have a air pocket in the system some place. It works fine with no load but put a load on it and then it shows up. It might also be a steering box problem. It's really hard to tell you what to do without seeing it in person but I would try to bleed the system more. Hydro assist might fix it but that still doesn't mean the problem does not exist.
I agree with this. Bleed it some more and see if it helps.
I had a bad box once (new reman) that was hard to turn but only one way.
