I thought that was what you were asking...how to make a locomotive stall. You pushing down on the locomotive is the same thing as adding a bunch of extra weight to it. The steep grade contributes being reducing the number cars required to make the motor stall...which is only an issue if it has too much weight. Most models, by design, don't weigh enough to stall. The closest I've seen an unmodified factory engine come to stalling was with my first athearn PA-1...actually...all three of them. They were underpowered...and sucked current like no engine I've had before or since. They'd sometimes get heavily bogged down...sometimes close to a crawl.