Fuel guage jumps from Full to Empty

I have a 2000 Jimmy/Envoy and my fuel guage fluctuates randomly from full to empty and back. Is it the Fuel Sender, or could it be something-else? Any help would be appreciated.

I am moving this post to the Blazer forum, this is for the 2002 up newer model Envoy.

Its your fuel level sender. Its a common problem. Ebay has them often and can be purchased on there for really good prices, when compared to dealer prices. I myself recently replaced mine. Purchased it on Ebay for $20, compared to the dealer wanting $200 for the same part.