Is that from a bad heater core? There's no moisuture in the carpet that I can find, nor do I smell coolant. Maybe it is a bad seal on the windshield? I live in Seattle, plenty of rain, but the dew in the cab is mysterious to me, especially since it's been sunny 2 days in a row.

 

I'm just north of the border from you, I get the same thing in my dodge, lots of moisture on the inside of the windshield in the morning. It has to be something with the truck because my GM and Honda don't do it. Although, sometimes I can smell a bit of coolant??

 

I've gotten it from a leaky heater core, 3rd brakelight, windshield, back glass and a/c box drain.

Anytime water gets in, then evaporates because of warm sunny days, it condensates on the winshiled or other glass. It could be just the jute under the carpet is moist, but the carpet is dry to the touch. It still evaporates in the warm sun and does the same thing. It could be just the firewall padding that is moist and not the jute or carpet.

I always pull the carpet up around the edges, look very close with a flashlight and feel with a perfectly dry hand as far under as I can. You can trace it up to the front or rear to give you an idea of direction.

 

Easy way to find cab leaks is to tape off the exhaust vents at the lower rear of your door jams and pressurize the cab by turning the fan on high.
Spray soapy water on the suspect areas and you'll find any leaks.