I thought I recognized that picture... its my truck! (taken while I was replacing the shifter seat bushing)
Anyways, that hose is just a vent for the transfer case adapter (that forward section is not part of the transmission, it is the adapter between the transmission and the main body of the transfer case).
Assuming you have a V6 auto, that hose is PN 90904-45005 - but any old vacuum line will work fine.
-Charlie
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'99 4Runner SR5 Auto -
4WD swapped
'89 Camry Alltrac LE 3S-GTE 5spd
'17 Chevy Volt Premier
'16 Honda Odyssey Elite
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