I just took my 2006 Navi to a quick service oil change location. While there, they checked my differentials and transfer case fluid. The tech mentioned that the fluid in my transfer case is brown and looked like gear oil and that it should be red like the transmission fluid.
I had the transfer case fluid changed in the spring at the dealership, could they have added the wrong fluid? If it was the wrong fluid, wouldn't the transfer case be damaged by now, especially after a summer of towing my 5000lb traniler 1500mi?
ATF is correct for your T/case and it will change color with use and heat. Check it by feel and smell. If it is real thick and has a greasy smell it is likely gear oil and you might want to file a complaint with the dealership just in case there is any damage. Then change the fluid and save a couple of ounces of the old fluid for testing if you or Ford wants to check it.