I've also seen a few things that talked about a "fording kit", and that without such a kit it was limited to 30" (if I remember correctly). However, I've never seen the "fording kit", never seen it listed with a part number anywhere, never seen instructions for it, etc. I'm curious if it really even exists.
A lot of the stuff in the truck will run with water in it. To talk about it in a non-technical way, 12V doesn't have enough oomph to push through the resistance of water. Fire departments will often find cars at the bottom of bodies of water with the lights and other accessories still on, no problems. That brings up an important distinction... What depth of water can the truck continue operating in, even if it causes long-term permanent damage to the truck, versus what depth of water can the truck operate in with no long-term effects? You see that National Guard video, and you know the truck can do it (with poor maintenance and little preparation, probably including lacking the fording kit), but you know it destroyed that truck permanently.
I've also seen the number 50" published in a few places. I've always assumed that 50" is basically the bottom of the cab and cargo bed, so it has more to do with instability caused by water getting that high, or water flooding your cargo in the bed, than whether the engine can continue running.
