Trying to identify where this line (the black one in my hand) might need to go. Found it when I was replacing the check valve for an issue related to when I'm under load my vents default back to defrost until I'm no longer under load.

 

Have you traced where the other end is attached? That may offer some clues.
It's near your 4x4 vacuum modules does the 4x4 work correctly? If not it could belong to that system.
if there isn't a connection missing a line close to it, you'll have to follow where it goes and search for a vacuum diagram

 

It might be the vent for either the transmission or the transfer case. If so, it's normal.

As suggested, find the other end.

 

my 01 has the same line looked everywhere can't locate where it went its a clean cut so it didn't break off from somewhere ???

 

Obviously, you did NOT look everywhere because, if you had, you would have followed that line to where one end is connected. Once that is known, it can be figured out if the other end is supposed to be connected or if it's a vent hose and needs to be left alone.