The stock setup does pressurize all the fluid filled things on the truck EXCEPT the steering gear box in order to push pressure out instead of letting water seep in.
The engine, transmission, t-case, both axles and the master cylinder/brakes are all pressurized.
The pressure comes from the motors internal blow by pressure.
When the fording valve is cycled for fording, the pressurization begins and, according to the manual and eye witness reports, the transmission boot at the bottom of the shifter will inflate. This is an easy way to make sure the system is ready.
Since the bellhousing has an internal vent to the transmission, the plug has to be in the bottom of the bellhousing for the pressurization to be effective.
Lord send your Holy Ghost into our hearts and make the desire of our hearts Your Will.
Pro-choice, that's a LIE, babies don't choose to die!!