Hello, I'm very new to model trains.  I have a Christmas Village that I set up with a friend.  We are using two trains to enhance the village on two separate tracks.  Each track (EZ track) because we set it up and take it down after Christmas.  Each track has its own power pack.  However, it seems in places the train slows down and doesn't have the power to maintain a steady speed.  How can I fix this?