i have a chevy lumina 3.1 motor the fuel gauge does not work how do i fix it?

when i drive it will show a full tank of fuel but when i let it sit it will show how much fuel is in the tank but then when i start driving it it will show a full tank?

thanks,
matt

Might ask your dealer about whether yours has a fuel gauge module. Some did, to even out the reading and keep the gauge from bouncing around when the float moves. I think '97 was the first year for the module, but not 100% sure.