The CW80 may not be capable of powering the milk car. The milk car(and other accessory) solenoid inrush current can easily cause the CW to go into "foldback" mode, flashing the green pilot light. If you use the "uncouple" button to activate the milk car, then you have the track magnet added in to the current draw.
To test this, push the unload button while bringing up the throttle. The car should work, but obviously not as "snappy".