Just changing soles will not help. You probably catch all your body's momentum with a planted slide foot, and my guess is that you have fast feet (You have to wait for the ball at the foul line) and move a lot with your upper body (bent forward).
My rough advise: slow down your feet and let the pendulum dictate your stance. Ideally, you should synch your second-to-last step with the pendulum's forward motion, so that the slide adds its momentum to the ball. This will create both speed and help with release leverage.
But that's just a very rough diagnosis.
--------------------
DizzyFugu - Reporting from Germany
Confused by bowling? Check out BR.com's vault of wisdom: the unofficial FAQ section