Yesterday morning was tough because the Tahoe’s front blower stopped working, so defrosting the windshield was nearly impossible.
Googling revealed the problem was likely caused by the blower motor resistor pack. I got under the passenger side duct (just two screws) and removed the resistor pack (another two screws). Sure enough, the connector from the resistor pack to the blower was partially melted in several places.
The part was $51 at O’Reilly, and fixed the issue. The new one is a different design, so hopefully it will be less prone to melting — this is a chronic problem according to owners of GM pickups/Tahoes/Suburbans.