How old is your mainsail? I had the same kind of issues you're describing. I had an old blown out mainsail, and in any kind of wind the boat would be over on its ear (even reefed). I purchased a new mainsail last season, and it's amazing how much better the boat performs with an actual sail (vs and an old bag). Now when the wind picks up the boats stands up and sails, rather than being blown sideways.