Just for the record, I have an 06 340 Express, and the GPH your reading is PER engine. So saying it is only burning 12 or 15 GPH is false. That is x2. So 24 to 30 GPH. If she burned 12 GPH, at 28 mph, you would have 450 mile range or better. Not happening on twin 116 gallon tanks. Best you will get at cruising speed is around 220 mile range, and that is with 10% reserve or less.
Oh, and you have a double Fault on your Galvonic Isolator. In other words, your boat has a major electrical issue. Something is shorting out in the water. With the generator on or plugged to shore power, I would not want to be in the water within 15 yards of your boat. As a broker, you should really get the facts on the boat such as electrical failure and understanding GPH before selling it. Just my opinion.
