All of a sudden, the gas gauge on my '97 Altima doesn't seem to be
working properly anymore. When I fill up the gas tank, the gas gauge
can go only as far as between the 3/4 mark and the full mark. First I
thought it was the gas pump, so I tried several different gas stations
(over the last few weeks) but the results were the same. Does anyone
know what may have caused this problem? How expensive is it to fix?

Thanks -