I am using the basic Bachmann transformer that comes with most of their sets. The train is a Bachman 2-6-2 Prairie pulling 3 ore cars, tank and 2 gons. All of the cars are on metal wheels and very free wheeling. on the line there is a 2 inch hill that has a 4 ft climb. After running for 20 minutes the transformer gets warm. Is this normal? None of the smaller lines have this issue and they run the same size train, same transformer on shorter lines.