FWIW and not to be too pessimistic:

I experienced the notorious 'erratic/incorrect fuel gauge
problem/readings over two summers of driving (2003+2004). I tried the
Techron Trick as well as other fuel/injector cleaners/additives to no
available.

I also had a PCM??? re-program done (there is a TSB on this) which
attempts to reolve the problem as well TO NO AVAIL. (There may be
newer TSBs as well IO suppose; I haven't checked sfor over the year).

IN THE END/late last year I finally had a GM dealer replace the fuel
gauge sending unit in the tank. I personally had the opportunity to
INSPECT the old unit that came out of the tank and examined it
carefully for any signs of deposits. ('The rumor' is that excessive
sulphur levels in some brands of fuels is reacting with SILVER in the
contacts and forming DEPOSITS on their surface which is impairing
their ability to correctly signal the fuel level in the tank. SHOULD
such deposits be VISIBLE? Well, I don't know BUT all I can say is, I
could NOT see any signs of deposits on the contacts of the old sending
unit - the surfaces looked 'SWEPT' BRIGHT AND CLEAN (and normal to
me).

In any event, the bottom line: did the sending unit replacement help
(hope so/that it will 'cause I don't know what lese 'they' can try if
it doesn't) BUT - can't be sure BUT I THOUGHT I still detected some
small degree of erratic behaviour in with the fuel gauge.

I've heard of individuals who've had ALL this done (sending unti
repllaced) and STILL the problem did not go away...

My bet/recommendation: I bet is that Techron (et al) WON'T fix the
problem and that you may have to get the sending ubit replaced as I
did and (like me) HOPE that that did/will work.

But (IMO): DON'T get your hopes up...