The fuel sender is a part of the whole fuel pump assembly that goes in the tank right? I believe that in the 2000+ models you can access that from the trunk and it isn't a PITA like it was for the earlier units.
You can't buy just the fuel sender alone, you have to buy the whole pump assembly with it. Very expensive from GM.
Easy to change though. You will need to siphon the fuel out of the fuel pump canister before pulling it out because you have to tip it sideways to remove from the trunk floor opening. The seal is reuseable.