That will depend on your definition of "stiff". On my 5005 the steering pump is in tandem w/ the hydraulic pump. At low RPM the pump will not be putting out much pressure and therefore not assisting as much. Also, I always TRY to be rolling just a bit when I turn the wheels as I believe it to be easier on the steering/front end components.
Also, have you checked the fluid level? If it is setup like the 5005, the back part of the hyd pump is for the powersteering and it has a separate sump up on the left side of the motor.