You say you've been into the power steering box..Any you've already had the front end aligned ?? Here's a test :

Jack the car up leaving both front wheels off the ground...Fire the car up and see if the box turns the wheels to the left on it's own without anyone touching the wheel...If it does you need to center the valve body{ on top of the pump }by loosening the two bolts on top and tapping it over a little..This will center the valve and stop the pull to the left..