I recently upgraded the ringfield motor on an hst to a cd motor.The hst runs well with the c.d. motor, loads of power ,no derailments, no problems at points etc.The issue I have is that as the model moves the power car rocks back and forth across the width of the track. The rocking seems to come predominately from the rear of the power car where the cd motor is housed.I have checked as many things as I can think of with no success.I looked at back to backs,axles,bogie frames etc they all seem fine.Any suggestions would be appreciated.