fuel gauge problems

What is your question?

My wife keeps complaining that the fuel gauge isn't working properly. I have driven the car and sure enough the low fuel light comes on at odd times and the gauge will fluctuate wildly. I have already had the sending unit on the pump assembly (the olld one was definately shot) and it got better but still is inaccurate and the light still comes on. What could be the problem and how would I have it fixed? I kind of need to know what to tell the mechanic. Thanks