The new N/S 270 (20-21357-1)(Powered A Unit) arrived on my doorstep the 10th of June. The Non-powered A and the B Unit arrived on the 16th of July. The A unit was running fine. It's been pulling a consist of 7 cars in addition to the B-A units. Today it stopped running and/or pulling. I can hear the motor running but it can't pull the consist. The powered A unit will run, but it slows, stops, then starts and runs then stops/starts it's very 'herky-jerky.' It can no longer pull anything even the B-A units. All the features work. I oiled/greased it again, cleaned the tracks....no joy. I replaced it with another of my MTH engines to be sure the tack/signal was not the problem. The engine ran fine, pulled the consist without a problem. I have no idea why the N/S 270 is behaving as it is. Any suggestions as to what I can do, or should I send it back? Thanks.