One problem related to ignition has been reported for the 2003 Chevrolet Avalanche. The most recently reported issues are listed below.
My 2003 chevy Avalanche 1500 speedometer reads 30 mph when I'm driving at 70 mph. After I stopped the truck, shut off motor and took key out of ignition and restarted truck and began driving, speedometer read correctly again. Later, same day, speedometer started reading 25 mph when I was driving at 70 mph with traffic, had to gauge speed with trucks tach. Same fix worked again. Please go to web site topix. Net , there are 30 more people like myself with the same problem with their chevy Avalanche/tahoe/suburban speedometer.