I wondered kind of the same, I bought 2 x 2004 GTX 4Tec's yesterday and we filled the tanks. Spend a few hours on the lake today and neither moved any lower... stayed 100% full according to gauge. My guess was it wont start moving down until you are really getting lower? I figure we rode at 20-30% throttle around maybe 2 hours total. Clearly we used fuel, but just wondering since I dont think the gauges are like cars, showing accurate levels as it goes down. Am i wrong?