I went through this recently with my 05 TB; exact symptoms as you. I had the fuel sender replaced via that 50% coverage arrangement roadie mentioned, all fixed now. It is definitely a very common and widely known issue and I would suggest that should be your first course of action, assuming you don't have access to a quality scan tool to diagnose further.
IIRC, the bulletin covered 2005-2007 but expired at 10 years or 120k miles, whichever comes first. I had 82k, and just went by a dealership with my issue and they knew exactly what was going on and dealt with the 50% coverage et al without any real effort on my part. As roadie said, your cost should be in the neighborhood of $140 give or take.
If you're the handy type, you could drop the tank and replace the whole gas pump assembly or just the sender unit, GM has paid out 50% of the parts expense to some people after jumping through a few hoops. I don't know if you'd really save much doing the labor yourself but it is an option.