I went through an exercise in this whole fuel sender stuff about 2 years ago. My gauge always read "Empty" so I would always just keep it topped off. I ordered one off of Rockauto and this time it wouldn't read past 1/4 tank even when full. First thing I tried was running a new wire from the gauge to the sender and a new ground line and it worked. It wasn't adjustment, a bad sender or a bad gauge (it is the original), just poor wiring. Maybe I just got lucky.
Worked even better than my 99 Formula's gauge, when that sucker read 1/4 tank you had better be in sight of a gas station cuz it was going to be empty very soon.