Having posted here before on Chevy truck issues, I was hoping I could get
some information regarding my 2004 Chevy Impala.  The other night I was
traveling on the interstate at about 70 MPH.  The tach was reading about
2100 RPM.  A short while later I noticed that the indicator needle had
fallen to about the 5 o'clock position.  The indicator still seemed to try
to track RPM, but it certainly wasn't in the proper position on the guage.
The cruise control continued to work fine, and there were no sudden surges
or anything like that.  I've used the car several times since then, the
needle is always in the 3 to7 o'clock position and does move with RPM
fluctuations.  Anybody know what drives or provides the tach signal these
days?  Or is this more likely to be a faulty instrument panel cluster?  All
other gauges are working properly.  Any thoughts would be appreciated.  The
factory warranty has expired.  I need to research if this is something that
the extended warranty would possibly cover.  Thanks!