My son has a 1999 Chevy Malibu. About 4 months ago we replaced the whole fuel pump assembly and have had no problems and the car runs great. Stopped for gas on Friday and filled up tank and about 20 minutes after getting gas the fuel gauge dropped to empty and the low fuel light came on. I pulled over thinking I was leaking fuel which I wasn't and when I stasrted the car back up the fuel gauge read full again. It happened the same way yesterday on the way home from work after no problem for the drive to work. It seems the fuel gauge never returns to the right level when you're driving only if you stop and turn engine off and back on. When it happened yesterday and I stopped I attempted to turn off and back on with car in nuetral but the gauge stayed on empty but when I put car in park and restarted it the gauge read at the right level, not sure if this means anything. Drove car to work this morning with no problem at all.

I would check the electrical connections at the fuel pump. Is there an access panel in the trunk or did you have to drop the tank?

In my opinion there is no problem at all sometimes just electrical connections makes issue otherwise this is normal thing when got power all the sensors works fine.