Oggy, you have to have backspin...that's a good thing. I'd say more loft on your driver will keep your slice airborne longer and, hence, in more trouble.

My guess is that you are getting ahead of the ball, lagging your hands behind your body. Maybe even coming over the top a bit. You must be getting some good contact to nail it 255, so your slice isn't that weak.

Listen to your teacher, of course, but I had the same problem. My grip was too weak, I was getting ahead of the ball, and I was constantly aligning myself to the right, which only makes things worse. Also, I was standing too close to the ball. So I strengthened my grip a little, stood back from the ball and flattened my swing, shortened my backswing. The last thing I did was tee it higher.

Now, I can't slice the ball until I try extremely hard. I don't draw either, until I try to. Most of my mishits are pulls, or just the result of a 14-handicapper sometimes mishitting, chunking, or topping.