Trailblazer/Envoy checking/changing transfer case fluid

A how to for checking the transfer case fluid and also how to change it.
The transfer case is located under the drivers seat.
Tools required:
-3/8" ratchet, bit holder, and 10mm bit
-drain pain
-transfer tube
-white ziptie
-2 quarts GM Auto Trac II fluid
www.amazon.com...
It is NOT uncommon for a dealer/independent shop to top these off with transmission fluid. This is why it important to check it, especially if you are not the first owner and don't know the service history.
This service goes for in the $130 range at the dealer and a couple bucks less at an independent shop. You can do it for less then half of that, this includes buying the tools shown and the fluid.
It is recommended that this fluid be changed every 50k miles.
Also, a 3/8" bit should not be used. It is 10mm.