Chrysler Repair: keep running out of gas :-(, dumb question, town and country

Question
This may seem like a dumb question/comment.....but.....I have a 2005 Town and Country(love it)100K miles. My overhead display of how many miles left is wrong and now my gas gage on my dashboard is also wrong. It shows more gas than what I have. SO we have been calculating when we buy gas and then setting the trip back to zero. I should have plenty of miles left but I am running out of gas periodically. Maybe we are calculating wrong but could this be another problem. I dont want to take it in and spend $$$$$.
Thank you.

Answer
Hi Cathy,
Does the gauge show full when you fill the tank? And then as you drive does it seem to drop in proportion to how far you have driven, but that as you continue driving does it "hang up" at some point where the needle stops dropping and the mileage remaining reading similarly doesn't change very much? If so, that would be an indication that the mechanical float inside the tank is hanging up. That would involve dropping the tank down and removing/replacing the float mechanism or at least figuring out why it hangs up. Let me know if that picture I have suggested seems to be true.
Or does it seem to move smoothly across the range of the gauge as you drive (perhaps staying a full for too many miles) but once it starts to drop it does so smoothly but it is always optomistic about how much you have left, all which might be due to an electrical issue that might be corrected at a lesser cost?
Roland

Additional comment:
Thanks for the rating and nomination, Cathy. I tried in my first response to differentiate whether the issue was electrical only having to do with the wire that leaves the tank or was it a menchanical problem with the float level inside the tank not sinking as the gas goes down. So please re-read my slightly modified answer (above) and let me know what you observe from the time you fill the tank until the time when you get it re-filled.
Roland