I've made quite a few attempts at pulling sugar and each time I start pulling it, it becomes very firm very quickly and starts cracking before I can finish. I've watched YouTube videos where it seems like people have a lot of time to pull and shape the candy. I've tried several different recipes, some involving more corn syrup, some with adding vinegar at the beginning or at a specific temperature, I don't stir it once I add the corn syrup. I've used a cool room and a warm room. My equipment is clean. I've been cooking it to about 310 degrees. I appreciate any suggestions.