Here it is guys. This is a common problem problem with this vehicle.
This will save you huge money.
The problem is that the fuel sensor has gone bad. Not the whole sending unit. By the way the sending unit is part of the fuel pump. Its going to cost you around $400 to replace the sending unit/fuel pump. Dont do this. The dealer and all most all autopart stores will only sell you the whole sending unit, not just he fuel sensor. It took a little research but I was able to track down how to fix what is realy broken not just replacing expensive parts.
You can buy the fuel sensor off of ebay for under $30!!!
It attatches to your fuel sending unit. The part number is:
ACDelco SK1159 Fuel Level Sensor
Put this in the ebay search engine and boom you just saved yourself $1000.
This is all you need to fix the problem. You will still have to drop the fuel tank and pull the sending unit out of the tank and all you do is replace the fuel level sensor on the sending unit. For all the non mechanics out there this is realy not as hard as it sounds. It is realy rather easy and trust me you will feel a lot better about spending 29 bucks than paying the dealer a thousand bucks! Every time you see the fuel tank reading full when it is: priceless.
Here is some basic instructions.
2005 CHEVROLET TRAILBLAZER LS 4.2L 256cid L6 FI (S) DOHC_Fuel Level Sensor Diagnosis and Part Selection Advice: