I haven't been driving my truck much lately on account of having a winter beater, so it has mostly been sitting in the driveway, however yesterday I got in it to start it up and take it for a drive and noticed there was a fair amount of condensation inside the windshield and even on the gauge cluster. Inside the truck smelled a bit musty too. I felt the carpets because I know there are some common leaks and they were completely dry, and the headliner was dry as well. The condensation went away after only a minute or so of running the defroster on max. We have had some large temp swings (it starts around 30 in the AM, and ends around 50 in the afternoon, much hotter in the sun, especially in a vehicle), but it still seemed odd. Anyone have a similar issue? Is there anywhere I should check for leaks?

My truck is a 2015 Super Cab. No sunroof. It does have a rear sliding window.

 

Tough to say. Driven little lately, temperature swings create condensation... I'd drive it a bit more often before I got concerned, probably needs an interstate drive to charge battery as well.

 

I agree, I should take it out for a highway run to charge the battery and let everything get up to operating temp. I took a closer look again today, pulled up all the mats, felt all around the carpet and headliner and nothing felt damp. No condensation today.

I park on a slight downhill and I read that in a heavy rain, water can run off the tonneau and enter through the vents on the back of the cab. We did have some heavy rains a week or two ago. Maybe this was the issue?

 

Cool damp air trapped in a cold cab as the outside air temperature rises is a recipe for condensate and consequently mildew if left unattended. Ask any boat owner that covers his boat in winter what he sees come spring time.