How to fix Fuel Guage which constantly reading too high?

I was shirt of oxygen for sure....maybe car was too. I took it to 2 dealers and neither offered anything other than charging for a diagnosis, even tho car only has 70k miles. My own mechanic does not charge for a diagnosis- he fixs the problem or he tells me to live with the problem- which is what he said for this case. I know the sender is under the back seat and easy to get at. Once I get at it, what should I look for? Thanks.

Look to see if it has full travel up & down, may be binding. The contact or circuit board may be bad, might have to replace the sender assy. May try to operate by hand and watch the gauge, maybe see the problem as you move it.