A software update will not resolve this problem. I wouldn't do an update til you resolve it. Just one more thing to complicate the issue.
Most likely is a transducer going bad .... but could be the head unit ... you already checked connections the best you can. You could probably connect your unit to a G3 setup, but there may be some precautions to take. Maybe Rickie will check in and advise you about that.
Maybe someone else with a G2 unit will see this thread.
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Looking for the one that makes it all worthwhile.