Check if your ball count unit stepper spring is wound too tight or too loosely. An over wound spring can make it jump two positions. Also make sure the little catch mechanism on the steppers is working clean and smoothly, that is the other thing that can make those jump forward. Make sure the contacts on the wiper fingers are aligned and stepper board are clean and making good contact. I would think the Ball count/player counter units are going to be the problem based on the issues your having. I also know on ours if your not careful the playfield can whack the top of the stepper when your take it in and out.