i know egs are infamous for their fluctuating gas gauges, but mine is a different story than i have heard. when i fill my car, the needle doesn't go past 3/4, but i put in ~8-9 gallons, so i know its actually full. then as usual civics fluctuate around corners. mine does the same but changes up to a 1/4-3/8 of a tank fluctuation. could this be a bad sensor in the gas tank? if so how do you replace it? if not, what else is there to do?

 

the full tank indicating 3/4 indicates a bad fuel sender or bad gauge.
if you have the ability, use a volt meter and probe the fuel sensor wire. It should have a 0-5 volt signal on it. If it doesn't get less than 0.7 volts when the tank is full then there replace the seder in the tank.
If it hits < 0.7volts then the problem is in the cluster.