Electronics bugs can be a major pain but at least you aren't burning 300 gallons an hour!!!
I've met Troy, he has done work on Tobeck's boat and he is a sharp operatior on NEMA 2000 network issues.
One thing you might just try is checking your "device list" in the Lowrance setup menu.
With your key switch on, see if you can find the fuel flow sensor by its correct name.
Try to select it in the menu and check its configuration.
If your Lowrance is not correctly reading the sensor by name, or if the sensor is mounted backwards (fuel flow arrow points toward engine) it could lead to the false readings you're experiencing.
Good luck and let us know what you find out!