Try gmpartsdirect.com:
-> Tahoe
-> Instrument panel
-> Cluster and switches
-> Heater control
-> w/auto temp control
Enter that in your cart, and you should get a part number on it. Then you can verify that the part is what you're looking for. If you send them an email with that part number and your VIN, they should be able to tell you if it'll work (I went through a couple emails with them to verify some cross rails with Escalade racks)...
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---------- Post added at 03:53 PM ---------- Previous post was at 03:51 PM ----------
Found a diagram under "instrument cluster," and item #12 does, in fact, appear to be what you're looking for. Don't know if it's plug and play or not.