I have a new N gauge setup and I'm having trouble with various railcars disconnecting from each other as they go around the track. When this occurs the couplers are not matching each other in height. One coupler will be lower than the other so the coupled connection is barely made. The cars will separate as the train moves and flexes. I can't figure out how to get the two couplers to match each other.  Any ideas as to what is going on?