Juice, the spring pushes the plunger out pretty hard, never had a problem with ours not shifting. One of the things I always do on that style solenoid is, wire a pushbutton switch inline so when you are sitting in the lanes or wherever you can release the solenoid. When you pull back into low gear the plunger will always stay back as long as there is power to it. This will make the solenoid get hot, won't hurt anything but your arm when you touch it, the pushbutton allows you to release the plunger without having to kill the main power.
Curtis