The major causes of a slice in a person that has a proper, balanced setup is trying to hit the ball too hard rather than simply swinging the golf club. Generally if the rest of your clubs go just fine but the tee shots with the driver are the only ones that slice, a players is swinging too hard. When we swing hard, we grip the club tighter and tend to swing "over-the-top" resulting in the outside-to-in slice producing swing path which is further accentuated by the tight grip impeding the club release.

Make sure you have a square set-up (maybe even slightly closed), the ball is in the right position front-to-back, and swing easy. No need to kill the driver as the club is designed to do the work.