Worked for me... turned out to be the pass. window module
Thanks very much for your info. I thought the dreaded electricla issue on my 2000 GC was too much for me having all the classic symptoms so I just took it to the dealer and was charged $400 to be told the instrument cluster had a short and it would be another $1000 to replace. Decided I'd try an ebay cluster for $90 which changed nothing, so I then knew the dealer was attempting to start with the most expensive part and work down and it would cost me $1,000's in the end. I started out unplugging and replugging the modules on your list from easiest to hardest (ECM, radio, amplifier, inst. panel, driver window ... when I got to the pass. window and pulled the plug everything instantly returned to normal (instrument cluster went normal, a/c worked, readings on overhead display went normal, etc) ordered the $30 window module from ebay and all has been well for most of a month and 650 miles. THANKS VERY MUCH FOR YOUR INFO.
I am having an issue with the keyless remote not working, but that's nothing over the anxiety of driving with that electrical issue.