Laserdoc,
Not at work now until after the New Year to be able to check that serial number but I pretty sure with the unit containing the GR50 GPS Receiver that it also contains the large gauge power cable with the molded in filter as well.

This would also be the same power cable as was in the interference kit.

When you adjusted your transducer; did you try angling the back end down slightly? Sometimes this is all you need to do to get it dialed in.