2007 t600 hard to steer to the left but easy to the right

o7 t600 put main steering gear box on in November a rebuilt unit from kw dealer old one was just wore out.new done fine until may the at times it seemed it was extra easy to turn then it started getting hard to turn left at times both hands on wheel and all you could do to turn left but it was easy to turn right.replaced the box again fine until this week no problems to turn right but at times its hard to turn left its like the power steering pump going out but its only on left turns if it was the pump it should do it either left or right.please help so confused by it

 

will check thanks