Sighing sound seem to some from below dash on passenger side

The doors that control the direction of heat and air are controlled by either cables or vacuum valves. I believe your model has vacuum controlled doors so check for bad /cracked vacuum hose to the passenger side door underneath the dash on right side.

Sounds like one of your flaps in duct is stuck. Look for cable to air handler and see if it moves or is stuck.
FREE-PPV.com

Could be that the hvac control module has an intermittent problem or the air mix door control for the passenger side is sticking. Check for error codes (DTCs) using a code scanner, but may not show an intermittent mechanical issue. If you can get at the air mix control on the hvac box under the dash on the passenger side, you may be able to check its operation.

i have one in the yard but its late here and its a raging thunderstorm outside so have a look in front of the firewall at the bottom passenger side first

Does the sound stop after a minute or two? IF so, this is normal. When the a/c is working, there is high pressure on one side of the expansion valve, and low pressure on the other. When you turn the a/c off, the pressures equalize. That's the noise you are hearing.

your mode door sounds like it is not moving
the air distribution is control by an actuator(motor) that sits on top off a door that moves to distribute air flow to whichever setting you set it to-if the door is broken it will no longer move and will stay on one setting all the time-the same thing will happen if the motor is no longer working. the only way to be sure is to physically check the motor. this is located on your heater box which is the large black box that is under the dash on the passenger side(it very big-just look under the passenger side dash and you will see it)if the motor is not working-replace it-if it is working you will have to replace the whole heater box which can be a pain-usually the dash has to be removed.
hope this helps

Need more info: I assume you are talking about the side windows, right?
Do they fog up when the truck just sits? Does it make a difference what the outside temp is? Does it small like anti-freeze (sweet smell) in the cab when it happens?

The first and easiest thing to check is drain tube from the air conditioning unit. Air con units are dehumidifiers and the water that they condense from the passenger compartment is supposed to drain out. If the drain gets plugged, then the water sits inside a little reservoir under the dash on the passenger side. From there it goes right back into the cabin raising the humidity and fogging the windows. The drain can be easily cleaned by blowing compressed air up the pipe.

BOTH SIDES ARE CONTROLED FROM THE SAME COIL FOR AIL SUPPLY BUT IT SOUNDS LIKE YOU HAVE A DAMPER THAT IS NOT OPENING TO THE AC COIL. ON THE NEWER MODELS THESE DAMPERS ARE VACUME OPERATED SO I WOULD CHECK THE VACUME LINES FROM THE CONTROL PANEL ,ON THE DASH. IF YOU HAVE KIDS SOME TIMES THEY MAY LAY THINGS ON THE DASH AND SOMETHING SMALL MAY HAVE DROPPED DOWN AND HAS THE DAMPER TO THE DRIVERS SIDE BLOCKED SHUT. THIS IS NOT AN EASY FIX

Hi jrm the smoke under the wing is the fuel fired heater and is normal. the noise is the heater motors for the heater flaps, there is a jag fix but you have to replace all the motors just ignore it.  Try changeing the filter for the heater under the left side scuttle panel thats below the black plastic panel below the screen that will help the steaming up     D