About a week ago I filled my tank and got into my car and saw that the gauge was reading only 3/4 full. Thinking that the auto shut off of the pump didn't work properly, I went back to the gas station and attempted to add more gas, it only took 50¢ worth.

Ok now I thought the sending unit of gauge could have a problem.
So I continued to drive for the week using the odometer as a gauge.. I ended up removing the fuel pump assembly and cleaned the float contacts which have over 200k miles on them.
Cleaned the contacts with QTips and carb cleaner (sprayed on the qtip), I didn't attempt to clean the (I guess what you might call) the brush. I did get some brown varnish coating off the contacts. You can see wear on the contacts but I'm trying to save $70 plus dollars on a new part, so I gave it a try!
It seems to working properly so far..

This is about the 4th time I've taken this apart for other reasons lately.. But it's a pretty easy job (about an hour, taking your time), just be VERY carful, (pull the fuel pump fuse) you're dealing with gas fumes which are explosive! On a side note I saw a guy on YouTube using an electric driver to remove the screws securing the assembly, stupid move! I don't care if your's is certified spark less others may not be....

(The photos are of the sending unit are after cleaning.)

 

Welcome in,I had this problem with my Ford F-350 diesel and cured the problem with two bottles of Seafoam,one per full tank and it fixed the problem,a year later i had the same problem with the tank on a Corvette,same solution same fix,I usually put in a bottle of Seafoam once a year now in all four of my vehicles and no problems.