The above images may be pertinent. However, dropping the shoulder could well be the source of your problems. Because of the natural spine angle in set up, it seems as if your left shoulder 'drops' under your chin. In fact, it's just a consequence of rotation - the level of your left shoulder in relation to, say, your hips should remain about the same.

If you are forcing your left shoulder down, the likelihood is that you're then raising the left shoulder in order to help clear the left side. Unless you time this perfectly, you will either clunk or top a lot of shots.

What has probably cured your slice is a greater arc on the backswing. When you sliced, did you feel 'cramped' through the ball. This would happen with a very compact (i.e. too narrow) backswing as you then try to generate power on the downswing. You probably came too steep into the ball with the hands well ahead of an open club face and no real 'space' in which to release the club naturally.