Call them back as ask what status your order is in. That way you will know where your order is. If it's in BGL status, then it could be anything, as it just means that they are missing a part(s). If it's BX, that means they have all parts and just need to schedule the build. I feel as though the rep just made up the "Waiting for Cummins 600" to get you off the phone. It could be something like tow hooks or a radio that you ordered that is on back order. Remember, manufacturers use just in time for builds so if they don't have any motors, nothings going to get scheduled to built as I see others have been scheduled.