Try to disconnect the instrument cluster and see if the drain goes away. I had a battery drain that would kill my battery overnight. It turned out to be the instrument cluster. I send it off to automotive circuit solutions for repair. After i got it back no more battery drain. Worked for me but you may have other issues.
I had the random language scrolling on my 2004 Silverado Z71. I sent it off to automotive circuit solutions for $100 they did a full rebuild and installed blue leds. Issue is gone and service came with a lifetime warranty. Check them out automotivecircuitsolutions.com I highly recommend them.
I had the battery drain issue with my 2004 Silverado Z71. After troubleshooting the problem for several days I came across this forum and unplugged my cluster and sure enough my drain went away. So I sent it off to automotivecircuitsolutions.com and for around $100 i got it repair and upgraded to blue leds. Its been a week now and the battery never died. They have a 24 hour turnaround time and it came with a lifetime warranty, I highly recommend them.