You can also get a vacuum leak from a crack in the vacuum reservoir under the cowl. Ask me how I know

 

Where is that?

 

Down where the mechanism for the windshield wipers are.

 

Looked everywhere on my truck, I don't have one

Looked on line and it looks like a film canister?

 

Open the hood, see those grates at the base of the windshield? Toward the passenger side, under there, you will find the vacuum reservoir.

 

Didnt get around to that today, started the truck and warmed it up, when turning it off I heard a sucking noise inside the cab. Kinda sounded like it was right behind the climate control. Guess I found it lmao

 

Yep, pull the controls, have a look.

 

Sadly don't think that'll bring back my 4wd though lmao

Had a guy offer me a 1986 f250 with the 6.9 diesel in it today, thinking on it but I'm not sure.. I do like my diesels

 

Which line is the one for the vent selector, everything seems tight, jiggles everything and it kinda sounds like it's sucjing through my climate control, why did dodge make it like this, how hard would it have been for them just to take and put a cable from the climate control to the event selector

 

There are a selection of doors that the vent selector controls. Doing all that with cables would have been a drag. Easier to just use vacuum. (and cheaper too.)

Did you pull the HVAC control, and have a look at the backside?