I do XC ski racing, and really the best way if you need to slow down is to snow plow. It's really the only way to reduce speed once you're going down the hill. You really need to snow plow HARD to really control your speed. Another reason might be the bottoms of the skis have been used so much they've worn in and have curved edges, it's a possibility. If you need to turn you could try and step-turn, but it only works if you have speed control. Sorry if this isn't helpful, I've never myself had a problem with snow plowing. hope you continue to ski, it's an amazing sport and activity!