I have no issues with my GB Premium. I have an air ball protector on the left ramp and outlane covers. I don't feel like a center post is needed at all and I also wouldn't get carrot flippers as that will fuck with the geometry of the game.
A local arcade has one with carrot flippers and it feels like shooting bricks.
Maybe you need to just make sure your pin is level or maybe make some adjustments to your scoops.