zadaddy
+1y
I had a 98 tahoe that did the same thing. On the fuel sending unit assembly there is a float with an arm that runs against a rheostat (sp?), which in turn is transferred to your gauge to show you how much gas you have.
One of 2 things have happened.... #1 there is junk on the rheostat and it is not reading correctly or #2 the rheostat is faulty.
If you feel like you can change this yourself, you can get the sending unit from any parts store (I work at Advance) for around 300-400 bux tops.
I never fixed mine, just ended up selling it as is. I always used the x amount of dollars = y miles. Just be sure to take into consideration when gas prices go up