Gauges do go bad...I have a new sending unit and good grounds, but My gauge is goofy, have not replaced it. Full is full, and when first hits empty is half a tank. It drove the guy I work with on my car nuts, he is OCD and and was ready to explode. He adjusted the sending unit to do what it is currently doing, which will kill the gauge faster, oh well. I just keep track of when I fill the tank go 200 mile ans refill.
As long as the sending unit is good and grounds are good. Check Gauge they are old...and do fail.
