Happened to me once when the fuel sender busted on my old 1988 Grand Wagoneer. I should have been suspicious about that 3/8 tank indicated on the gauge lasting so long. I came across an old Ford 4wd pickup stalled at the top of pass on a trail in Colorado once. It was broken down. Another guy and I poked and checked a number of things when I noticed while under the truck that it had dual tanks and some loose wires. The fuel gauge showed fuel in both tanks but I had the driver switch tanks and the truck fired right up. He was just on an empty tank.
If it does turn out to be the fuel pump and it's located in the tank as others indicated, it's not too difficult to drop a tank if it's empty. However, if the tank is full then that's a heck of a lot of weight and you need a floor jack to support it. Shoot PB Blaster on the bolts and hopefully let it set awhile before unbolting the restraints and things will go a lot easier.
LOL. There is a maroon one sitting in my driveway as I write this. It hasn't told me the correct fuel reading in a year. A couple of my collector cars are the same way. I'm just too lazy to drop the tanks to fix them. I just make sure I fill up whenever I go for any distance.