cooler air via the vent?
 

What drove me nuts about my old car was that the air coming out of the vent was much warmer than outside air, meaning it can be pretty miserable driving on the highway with the vent on instead of the A/C.

Now it turns out my new truck is even worse. It seems like the air from the vent 10-15 degree than the outside air. Are there any modifications I could make to allow cooler air into the cab via the vent? Where exactly is this heat coming from? Come to think of it, where exactly does the air from the vent come from?

warm air from vents
 

the reason why your air is so warm is probably because it has to go down past the firewall, WHICH IS WARM. the fan in my car is right behind the exhaust header on the ENGINE side of the firewall!! But i don't have to turn the fan on to get warm air in winter. i just turn the heat control up and let the warm air circulate through the car naturally. If you want to get cooler air maybe you could fab a heat shield for your firewall/fan area to cool things down, or maybe put your fan under/ behind the glove box like some other trucks. Maybe you could post pics of fan area. the intake for the fan is usually by the wipers so it would probably help to install heat shield.

So, I looked under my hood, and those air intake areas right in the back below the windshield are where the vent goes in? And the metal plate at the back of the engine compartment is the fire wall? If that is the case, I think I could easily put some fiberglass insulation between the engine and that firewall right around where the vent is, but won't the firewall get warm from conducted heat as well?

Trucks used to have vents at the floor which would pull outside air from under the truck. Maybe you could rig something similar.

Then you increase the amount of exhaust you suck in

I believe those pulled from the front fenderwell. I never noticed an exhaust smell.

From other cars I mean. Seems like you'd be pretty close to where everyones' tailpipes are

heat
 

If after running the engine and then turning it off,hat may stratify under the hood,exposing that region which contains the fresh air ductwork to this heat"flux" and raising temps of fresh air once you drive off again.------- After a period,the cooler incoming air should carry off this heat( unfortunately onto you).then settle out at a discharge temp closer to outside ambient temp.--- If you can take the heat for awhile it will go away.