You cannot assess this when the truck is parked. Everything (the life support systems) will work correctly UNTIL the vacuum noise comes, then the system will default away from the current vent selection to the windshield vent selection. If this is your symptom, then you really need to be looking behind the battery tray for the blue/white check valve, and repair the broken hose that goes to it. Engine load changes the vacuum, the change in vacuum changes the flap settings inside of the ventilation system. You can hear it as you drive.

 

The vaccume noise i hear does do it in park as well though, not just while driving

 

Sorry, I missed that part. You get all of the available flap positions? My truck would give the flap position I selected until the engine load increased to the point where the vacuum went to neutral, then the flap changed to the windshield position, there was an air leak noise when this happened.

 

The air works as its supposed to with engine under load or in park, i hear the noise when i rev it to about 2300 rpm, it sounds like a very loud hissing noise in the very back of the dash, i took off the oval shaped cover and cant see where the noise is coming from, sounds like the verrrryyy far back of dash but not in the engine vay, but right before the firewall

 

Also when it shifts gears, like right after it shifts it stops for a second and then continues

 

Bump

 

Stilll needing help