It's a Pain in the rear getting to the gas tank... There is alot to be done and it's time consuming. Hate to put a damper on things, just letting you know... Anyhoo, I would have to say it's the sending unit inside the gas tank. The fuel gage itself just reads the information being sent to it. The sending unit has many little contact points that create connections as the float moves about reading the different resistor values. There are also a few wires inside the sending unit that may have potentially came lose.
To remove the gas tank, here are the steps. I have done it and have pictures on another board to assist if need be.
BEFORE you mess with the gas tank, make sure you don't have a full tank!!!!!!!!!!!!!!!!!!!!
1. Jack car up.
2. Remove rear tires (Use the E-brake to keep them still if you need to break the lug nuts lose).
3. Remove the car battery.
4. Drill out the 3 rivets on each fender.
5. Remove each black plastic fender insert (Pull out all of the little black plastic tabs first).
6. Here you can access the fuel lines on the drivers wheel well. Remove them now if you want.
7. Remove Gas filler tube from passenger side fender well and the vent tube (Siphon any leftover gas for ease of removal).
8. In the trunk, drill out all of the rivets in the square pattern on the gas tank cover / shield.
9. Remove the plastic gas tank cover / shield. (Using a puddy knife will cut through all of the glue on the back of the cover).
10. Remove the 2 screws holding the metal gas tank straps in place.
11. Pull the gas tank back through the trunk. (You may need to push from the other side of the tank, back inside the fender wells).
12. When tank is in the trunk, remove the electrical connectors on the sending unit and make sure fuel lines are unplugged from drivers side fender well.
Let me know if you have any questions.
After pulling all the plastic push pins on the inner fender wells/skirts, you can bend them down out of your way to gain access to the fuel tank. Just my 2-cents. 
