Chris where is the neddle on the gauge pointed at? I dont want to sound like an a$$ but a little more info would be an excellent idea to help us pin point your problem.
Mine gauge stuck just below half a tank a few months ago. Discovered that the hard way - ran out of gas on the highway. (And I thought I was getting great mileage after the last dyno tune - LOL!)
We had installed a 255 lph fuel pump a couple months before. Turned out the pump turned in the bracket causing the rectangular sock/filter to block the float from going down.
Drove around with a couple gallons of gas in the trunk until we had a chance to drop the tank and pull the pump to fix that annoying problem.
Have you removed the gauge cluster yet to make sure everything is connected? If you have a spare cluster you could try swapping out just the fuel gauge itself and see if that has any effect. Other than that you could check the wires the go to the pump to see if any of them are corroided(sp) and fix them.