Answer:
Hi,
95% of the time (or more), the problem you describe it caused by the Fuel Level Sensor, which is mounted on the fuel pump assembly. This assembly is mounted inside the fuel tank (at the top), so the tank will have to be drained and removed to replace the sensor. The 'good news' is that the sensor can often be replaced separately from the entire assembly, so it is possible to keep the cost down, at least a little.
Good Luck, Greg