Fuel gauge won't show full

[YellowMenace]

I've searched and found some wierd fuel gauge problems, but didn't see this one. Gauge seems to work, except that it shows between 1/4 and 1/2 tank when it is actually full. It goes down proportionally from there as the tank empties.

Will show full when key is turned off. Replaced the sender and fixed the previous problem (pierced float). Tries old sender manually and it does the same thing. I'm sure it's in the gauge itself.

Any ideas.