Sorry i cant help you out there, but i just have to say that im havin the same problem. i drove about a mile and my gas guage went from reading an overly full tank to about a quarter of a tank. lol
i usually go off of my trip odometer, but the strangest thing happened about a month and a half ago. i went up into the hills and wheeled it pretty hard. Me and everything else in my YJ was bouncin around. Then i noticed a few days later that my fuel gauge actually read an accurate amount for my gas.
This lasted for about a month, and i fell back into old habits again of reading my gauge instead of my millage. And of course out of the clear blue sky it stopped working and i ran out of gas in the middle of town.
i still dont know why that happened.
My only suggestion would be to go up and wheel your jeep and dont come back until it starts working. lol or just wait for someone to tell us what the problem is.