A few possibilities.
1. Your float on the fuel sending unit came off.
2. Your float arm is stuck at the top.
3. You have an electrical issue that has the signal line form the fuel sending unit shorted to either power or ground (I'd need to see a wire schematic to see how it is wired)
4. Your dash gauge is bad.
First crawl under the Jeep and try to disconnect the fuel sending unit wire harness from the top and see if that makes a change. IIRC is should go to empty. There may be a junction connection along the frame that will be easier to disconnect (will have the wires for the fuel sending unit, tail lights, wheel sensors). Follow the wiring from the tank forward to find it. If it drops to empty, then your problem resides in the fuel sending unit (best to disconnect at the sending unit). No change, then you are back to a short in the wiring or bad gauge.