john-more than likely the sending unit in the gas tank.  I've done many
on that era s-10 blazer.  Gm will have the part-not sure about the
aftermarket.  I've also read where GM's top of the line fuel injector
states on the bottle that it helps gas gauge issues like this but
haven't had an issue since I read this.  Good luck.  Lastly-does it act
irratic at other times also-ie showing full when it's half, etc.
jerry@peru-motors.com

 My 2000 Chev Silverado LT 4x4 Ext Cab has an intermittent Gas Gage
prob.

 About 5% of the time it reads zero when tank has fuel....  95% of

 time it reads perfect....      Restarting the truck once usually fixes

  the pending prob.     Truck is 6.5 years old,   73,000 miles.

  I do like the truck a lot....   Still performs to near perfection!