If you already have a 3" Rancho lift and want another 3-4" than yes you are going to need new shocks. However wanting 6-7" of spring lift to run 33's seems a bit foolish, and will look really funny.
If you just want to rebuild the springs you have now and get an additional 1" lift and better ride quality, the shocks you have now will be fine. You can always buy longer ones when the time comes to replace the ones you have now, or when you have the extra money to do so.
