2004 lasabre speedometer & tach malfunctions

My 2004 lasabre's speedometer and tach malfunctions. They will work for an hour or so, then begin to either advance their readings. For instance at idle the tach will show 5000 rpm. The speedometer will show 100mph at normal cruse speeds. Is this an instrument cluster problem or the computer? Or some sensor?

HELP

Welcome to AF! The tach signal comes from the ignition control module (white wire) terminal E, and the speed signal comes from the vehicle speed sensor (VSS). It would be highly unlikely that both of these would fail to operate at the same time. This does indeed sound like a problem within the IC. Time to make some calls to your local JY!