May be, have you had the dealer re-program it for the new fuel formulation and the cleaner run through it?
have not been to the dealer yet, added a bottle of techron today, thought I'd run it for a tankful and see if it improves, seems to be highly recommended. now a nor'easter coming in so it'll take that much longer. enough of winter already! is the reprogram needed?
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...
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