Just a wild thought, sounds like the lane bed you are bowling on is changing the surface of your ball to a grit that leads to over/under, whether that be 3000 or 4000 or whatever.
I feel you just need to make a big jump and not try to skirt with the exact line between great reaction and over/under. Start with a 2000 pad, give it a shot. Then 3000 if that is too much. But try to get something you can reproduce by hand. Surfaces can change quickly so being able to make surface adjustments before you start will make the ball's performance much more consistent which will give you more confidence in the ball.