fuel gage on 2005 dodge caravan?

[raiders 1]

i have a 2005 dodge caravan i have a fuel gage problem don't know if it is electrical or the gas tank floater. every time i fuel up and mostly when i get on the freeway the fuel Gage starts moving to empty real fast like its wasting a ton of gas ,but then i park at work by the end of the day when i get it started again it goes back to normal,what can it be