I had this exact same problem and the only thing that helped me was adopting the "Moe Norman" address of dropping back about a foot back behind the ball before starting my backswing and them on the downswing, always keeping my right cheek back, until after I contact the ball.
Those two simple changes straighted me out, as I may only slice once or twice now a round and then it usually is a minor slice. I don't hit it as far, but more than make up for it by not losing so many golf balls and strokes. I went from losing 8-9 balls a round to one or two. I also hit my irons a lot straighter with more solid contact using Moe's method. I picked this up after watching Utube videos of Moe and analyzing his swing and then trying it on my own.
I have only been playing golf now for about two years, and am 58 years old. I started out with regular golf lessons, but they didn't help me with correcting my slice, as I also had a tendancy to swing too hard with the driver and tense up. Moe's swing corrected this problem automatically.
I had to learn to do it on my own with this different address and swing thought. Simply Google "Moe Norman" and you will see what I am talking about. I would try this before buying a new driver.It costs you nothing but time...and it worked best for me of any type of training, videos, or book instructions.