Often in higher windspeeds drivers crack the main or ease main traveler witout a corosponding ease of the jib. This causes lee helm and is easily corrected by easing jib to match. The inverse of this is also possible if the jib leads are too far outboard so the jib is luffing going upwind because you are overpowered. You can also try moving body weight fore and aft to ballence the helm.

Eric