Ah yes.. the Lumber Wagon!
We both be on to something. Me being that she is hammering the device pretty hard, and you with the fact that that particular model might have some piece in some tiny little spot that is not conducive to said named lumber wagon rides!
I have OCD "Obsessive Crappie Disorder"
In this situation I would call Lowrance and ask to speak to a head tech,not the general phone guys and discuss it with them.2 units going bad on the same boat is unusual.