[giffo]

Dealer doesn't know anything? Yeah.

Try to find (on the web) a copy of:

Technical Service Bulletin 07187C, issued March 2009. Campaign - Instrument Cluster Warranty Extended

Even if you can't find a complete copy of the TSB, again approach the "I dunno" dealer and suggest they check their records for this particular document, which they must have "overlooked".

Can't guarantee that you/your vehicle are covered, but check it out. At least GM acknowledges that there's a problem even if your dealer doesn't.