Alright. So the instigation of the problem seems to have occurred when we tried to cold start the truck at -40 F, or thereabouts. Initially I'm told it tried to turn over, but failed to start. From that point, on subsequent attempts to start the truck, it failed to turn over, and even the door chime started to grow fainter until nothing even turned on in the cab on the ACC and Run settings of the ignition switch. We've tried swapping relays, checking fuses, replacing the ignition switch, and of course charging the battery. Since charging the battery, something has caused the battery to drain again, and so I'm going to charge it again today. Thanks for your help.

i now suspect the Ignition Switch Accessory contact is worn out and losing Contact. All Instruments are sometimes dead and Heater/AC Blower sometimes inoperative at the same time.. Since Odometer info is stored in the Instrument Cluster the mileage is no longer true. This problem is definitely both a Safety Hazard and a royal pain in the butt. Due to the fact that 268,8XX Miles are on the vehicle it obviously is not a covered item. However it is a Safety Hazard to not having a Speedometer..

The JUNK Stepper Motors in the Instrument Cluster that were Original Equipment have been a notorious problem in ALL GM Vehicles in almost all vehicles GM produced since their inception. I have bought upwards of 15 GM vehicles and this one has been plagued with gremlins.