I have been trying to run multiple GP40's on my layout from the start. I have a relatively short manifest however I really like the look of 3 loco's. I have speed tested and matched them, and have also upgraded my controller for higher output. The problem is that they run good for several weeks and then one of them will start dragging the other one down. How can I correct this problem so I can run more than 1 loco and pull my full manifest of 16 cars which includes a track cleaning car?