[DCFriscoTX]

This is an older post, but I figured it might help someone Googling.
I have a 2006 Trailblazer with only 36k miles. For the last 10k miles, I had been getting poor mileage (17 - 18 mpg Highway) and I was told - normal for this truck. Also, it had been to the dealer several times for check engine lights, sputtering, injector cleaning etc. At 36.5k miles, the fuel gauge started acting erratically... Full, totally empty, and everything in between within seconds. Engine sputtering, check engine lights, etc. Was diagnosed as FSU. Since I was outside of warranty by 500 miles, Chevy told me that it was not covered by the warranty... Parts cost $130, but dealer p&L was close to $500... I went the route of cleaners, etc... did not help. Honestly, I was close to trading the truck due to reliability and poor mileage...

After a little armtwisting, GM agreed to replace the fsu free of charge as it was so close to being within the warranty.. the minute I got it back from the dealer, I noticed a jump in the responsiveness, performance... my mileage is at 23-24 highway.... where it should be.

Lesson learned... fsu is not just a fuel gauge sender... apparently, its issues caused the engine to go into a limp mode. Dealer tech said that it was common and issues had nothing to do w sulfur deposits..

My advice (from experience), if you are having issues and are within warranty, jump on it... i was told that replacing the unit yourself was not advisable... have to remove braces and take down the tank.... can be dangerous and is not for the rookies.