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Tahoe & SuburbanThe power, space, and brutal towing ability make the Tahoe and its longer sibling, the Suburban, arguably the best full size SUV's on the market today.
It would be behind the right rear wheel where the AC and Coolant lines enter through the floor. You can see in the diagram where the blower is and it is directed through the evaporator core and the heater core depending on where the air flow is directed by the HVAC Controller. I'm assuming that any water runoff would run out the bottom of the Evaporator which is labeled #5 on the second diagram.
The other thing to check is the wire loom at the top of your rear hatch where it enters the body. If not seated correctly water will enter here and run down the back of your trim onto the floor in that same area as the AUX HVAC.