Anyone have experience troubleshooting a sounder setup with a Garmin GSD 22? I have one connected to a GPSMAP 4208 and an Airmar B60 tilted-element through hull transducer and it's not working well I intermittently loose live bottom with the depth readout blinking. While it never held bottom well at higher speeds, it now looses bottom across speed ranges (idle to WOT) and at various depths (4 ft to 100+). I also have a paddle wheel speed sensor attached to the sounder; the speed sensor always reads 0 MPH. It turns freely but I have a replacement paddle wheel to see if it's just worn out. I've checked the sounder and xducer connections and they appear tight and clean. The lights on the GSD 22 show normal operation and there are no error codes on the MFD. I contacted Garmin; they said it could be the GSD 22 or the transducer going bad. They sent me a transom mount transducer to check it (free - very nice of them). BUT...I can't really check it's operation with the boat on the hard. Once it goes in the water, I can't really install the transom mount if the through hull xducer is bad without a haul. If anyone has some experience with a similar situation it would be great to know how to proceed before we go back in the water.