I'd like to see an answer to this question, but the bad news is, its most likely the display tube that has failed. I took mine apart and I can measure the voltages going to the display, and with work, even determine what segments should be lighting up in the tube, but the tube has failed and I can't find a replacement.
Ebay and junk yards are the place to look, the part from GM is $500+
here is the part #:
driver info display module '97: 12530327 $506.98
'98-99: 10436818 $340.90
'00-05: 10307106 $340.90
You can get them new from gmparts online for about $200. I've looked for two years in ebay and junk yards with no luck.
John