Keep in mind the Grudge has a very aggressive coverstock. It might not be going too long, just burning up too early and leaving nothing for it's move to the pocket. You may want to have the Grudge polished first and then see what kind of reaction it gets. Then if it's not something you like experiment from there with 4000, 3000, and 2000. 1000 is already one of the lowest grits a lot of people use so there isn't much room to go down from.
If the ball has a good amount of games on it you should consider getting the oil taken out of it as well before the surface adjustments.