A plow will also draft to the left side if it is not leveled fore and aft. When plowing, the plow should be level front to back as well as side to side.
Some plows have a rolling landside (tail wheel) that prevents excessive wear on the bottom landsides.
What about your tread setting on the tractor? Is the furrow wheel set to give the plow a proper width of cut?
Is this a drawn, mounted or semi-mounted plow? If drawn the hitch may be too far to the left causing the plow to pull crooked.