Hi Doug,

Serial data from the PCM tells the Instrument Panel what to do.  Since you have other strange temp related anomolies, I would not suspect a connection or IP issue.

Most likely, the PCM is getting incorrect inputs or has a defect.  To continue, you need special tools and expertise, to avoid making a costly mistake.  At least a scanner and good information system.

Let me give you a couple of links. 

This one will help you find a qualified professoinal to take care of this.  This would be the most cost efective option.  Shops on this engine are members of the International Automotive Technicians Network:

http://www.iatn.net/dir/search.asp

If you still want to tackle this yourself, you need information.  You can get access to systems information on line.  While this may not help you to diagnose the issue, it will give you an appreciation for the complexities of your ride and serve to illustrate the value of a pro in this situation.  Here is a link to ALLDATA DIY Online:

http://www.alldata.com/vehicle_owner

Thanks for the follow up, Doug.  The T-stat may have been sticking intermittently too.  Glad you got it taken care of.