Looks like a lens issue, not a camera issue!
http://www.usa.canon.com/cusa/consumer/products/cameras/slr_cameras/eos_5d_mark_iii?pageKeyCode=prdAdvDetail&docId=0901e02480532d6b
http://www.usa.canon.com/cusa/consumer/products/cameras/slr_cameras/eos_5d_mark_iii?pageKeyCode=prdAdvDetail&docId=0901e02480532d6b