This dose not sound right to me. Of course I seen worst problems out of the box but MTH product line is usually pretty dependable, as is Lionel and all the rest.
Go on line to the MTH web site and in the talk to us pull down you will be able to send them an e-mail. It might take a few days for a reply but they should be able to help you.
It sounds like a drive train binding issue to me.
Good luck