I do the same thing but not as much as i used to. The reason is taking the club to far on the inside on the takeaway as suggested. I have almost now got rid of it but it has taken me twelve months to do so. I bet when you hit pull shots you hit them absolutely flush, the reason you do this is because you compensate with your hands and wrists. I concentrated on keeping my hands quieter and turning my shoulders correctly on the takeaway. When you go to the range try hitting fades (at first you will not be able to), hit from the right hand side of the range (i always warm up from the right hand side of the range before playing) if you are a right hander. If the practice fairway has a tree on the right hand side try hitting fades around it. At first you will constantly hit pull shots because of the inside path and the fact there is a tree in your way, dont give up.