So due to some electrical issue which I can't seem to determine the cause of I now have a self-regulated odometer in my Suburban, here's how it works:

If my headlamp control switch is set to 'Auto' (which it is by default at startup), my DIC and Instrument Cluster are completely off. This results in all the gauges being dead including the odometer. The result is that my odometer will not record mileage while my headlamps are set to 'auto.'

If I switch from 'auto' to 'parking lamps' or 'headlamps' then my DIC and Instrument Cluster are immediately revived and all gauges begin to work perfectly.

I've also noticed that if I am in the 'auto' setting and I drive into a dark parking garage and my headlamps come on due to the darkness then my DIC and Instrument Cluster begin working again as well.

It would appear that I have accidentally stumbled upon a way to self-regulate the odometer in the Gen III Suburban. The big negative to this is that whenever the DIC and Instrument Cluster are working properly, the HVAC blows hot air only. Conversely, when the DIC and Instrument Cluster are not working, the HVAC works correctly and will blow correct air temperature according to its setting.

Has anyone else had a problem like this? I'm more mechanical than electrical but it would seem to be the problem must be in either the fuses, the relays or in the headlight control switch itself. I am leaning towards the relays simply because of the strange correlation with the HVAC system.