What is your gas gage saying? Is it staying on F all the time?
It's quite possible you have two problems.......the fuel sender may be bad and giving you bad fuel level readings....
Also you may have an evap problem where the system is not opening up(venting), and not allowing air to escape, through the vent valve, as you fill the tank with gas.....the other possibility is a plugged canister, kinked evap line,
bad vent valve, etc.