The fuel sending unit could be at fault or perhaps a short in the circuit somewhere. Also be sure to check the connectors at the fuel pump for corrosion.
I recently purchased a DX Coupe (Automatic), and every time i take a sharp corner or im cruising on the freeway with dips here and there, the fuel gauge goes up and down, more critically when the car is going around a corner, like a clover leaf ramp.
