Interesting...
My HUD has gotten very dim but still functions without issue. I can't see it in daylight hardly at all any more, but I still see it at night.
Performance shift is fine. As you may know, the indicator light for P.S. mode in 98's is on the dash (not the DIC) and it still functions properly.
Trip Calculator? I don't have one of those. The DIC in my 98 shows MPG, fuel used, oil life and range. For a brief few seconds at startup (before the zeroes take over, the info will display on the DIC correctly. It doesn't seem to be keeping up with the fuel-based items but the oil life is still ticking down at what seems like an appropriate rate.
I'm wondering if the fuel sender mentioned by BillBoost might be the culprit. Still, that wouldn't explain the TCS and ABS lights staying on steady and once in a while flashing. When they flash, the DIC starts working again.
I may just bend over and take the car to the GM dealer nearby for diagnosis. Will let you know what I find out if I do.