Tank Filler Pipe And Cap problems of the 2007 Chevrolet Trailblazer

The fuel gauge level indicator just went from "full" to "empty", it just went that fast. Minutes before it had just been filled at the gas station. When starting, the gauge rises then falls to empty. On occasions the warning message, "please tighten gas cap" comes on. Now months later, same problem; after contacting "gm" hotline, they still have not shown any concern. I keep track of miles driven since last fill-up and gas used, so I know when it is time to fill-up. I have read many same complaints, and I wonder why "gm" has not issued a recall. It is now 08/21/2012 and problem is still ongoing. Can you please help. Please. "gm" has on numerous occasions suggested that the wire harness on top of the gas tank needs to be replaced, to do so, requires a five (5) hour visit and they expect the customer to pay half the cost. Please help.