Mystery hose behind intake manifold ‘06

[Cdownhour]

I was changing my intake manifold gaskets and was alarmed by this capped off hose behind my intake manifold. (I have attached photos... let me know if they don’t show). My vehicle is operating normally so it seems to be an intentionally capped hose, but what is it?? I couldn’t find info regarding the line direction... and also, there are those three empty bolt holes right next to it that appear to be for an aftermarket part. Any insight about this system would be greatly appreciated. (My guess, hose for trans, and that empty spot is an upgrade option, i.e. pump, since it’s a closed system)

 

[boominXplorer]

Transmission vent tube has a push pin in the top to let air in and out but keep out debris.

The heads are cast the same so that 3 bolt port is the same as where your thermostat housing bolts to.

 

[Cdownhour]

Transmission vent tube has a push pin in the top to let air in and out but keep out debris.

The heads are cast the same so that 3 bolt port is the same as where your thermostat housing bolts to.

Thanks for the reply. The casting symmetry makes since for those bolts.
That hose is plugged with a plastic push cap, like the ones you find on fenders and such, so it can’t be the trans vent. I’ve seen that same hose capped the same way on videos of these engine tear downs. But no one ever mentions it.