I have the same thing with my tank. xb03 30 gal. Thought it might be the gauge or sender. Called Allison. Here's what I learned. First, they're made that way to insure you a reserve. Can you change it? Possibly. About 97 they changed senders from a float & arm type to a tube type. My tank measures 17" from the bottom of the tank to the mounting surface of the sender. If you have the arm & float type you should be able to bend the arm to put the float closer to the bottom of the tank. It will probably take some running before the gauge leaves Full but it will be more accurate at the bottom. Essentially you'll be reading the bottom 24 or so gallons rather than the top 24. Mine has the tube type sender with a float and magnet inside the tube. There's a circuit board in the tube that reads the position of the magnet. The tube is only 14" long. I have over 7 gallons when the gauge hits empty. I ordered a 15" tube, the longest they sell but may not use it. I'm going to experiment with the old one and a float extension. I make all short runs. No gear, one battery and no troller. Almost always leave with less than 1/2 tank. I like to go as fast as I can. I'd much rather be reading the bottom 1/2 accurately than the top 3/4 then nothing. If my experimenting works I'll post what I did. It may be a while. The boat is in my carport awaiting a mechanical trim gauge and a new prop. Threw a blade off by beloved SRX 29. Also a Brutaco ACU. Gotta raise the limiter.
