I'm having the same problem. The word on the street is GM will fix it under warranty if it was manufactured before 12/04 and has less than 70,000 miles. I took my '05 to the dealer and they quietly acknowledged the extended warranty on the instrument cluster.
2005 Chevy 2500HD, CC, SB, 4X4, Duramax, ARE Topper, 60 gallon RDS toolbox/tank combo, Kennedy Headlight Booster, Isspro pyrometer and boost gauges, EGR Blocker, PCV Kit, Bilsteins, 265 Michelin MS-2, TTS Exhaust, pulling 35' Jayco travel trailer.