Steering Holding up when I turn right.

[fossfactor]

Recently I was towing my 9200-pound trailer with my 2020 6.7 2500. When I turn right the steering wheel would lock up near the center. I put in two ounces of power steering fluid and this helped.
My mechanic could find no leak and could not replicate the problem. Any ideas on what it might be?

 

[jetrinka]

Only when towing? Are you using a weight distribution hitch with friction based anti-sway?