Are there any other areas of the floor wet ? Do you have the factory rear sliding window ?

 

I’d recommend pulling the fenders off along with the cowl.

Put a bead of silicone along the body panel overlaps where the factory put the adhesive. You’ll see what I’m talking about when you pull everything apart.

I had to do that in several places to keep my cab dry. It’s not a bad job just annoying.

 

Several years ago I had a really strange situation in my 2008 extended cab Colorado – I too thought that I must have a leak in the front area of the cab since the passenger side floorboard would seem to be the only area that got wet when it rained either fairly hard or for a long time.

But it turned out that was only where the water was pooling and further investigation showed that the water was actually coming from the rear of the cab. I checked the high brakelight but didn’t find any problems.

It wound up being a small pinhole in the passenger side groove that the molding sits in – actually just above the rear window, on the vertical part of the roof near where it curves back in to recess for the window. I had to remove the curved end piece of the molding to really see it and fix it.

Once I patched the pinhole, no more leak!

 

Put a bead of silicone along the body panel overlaps where the factory put the adhesive. You’ll see what I’m talking about when you pull everything apart.

I had to do that in several places to keep my cab dry. It’s not a bad job just annoying.
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This is what I will try thank you very much I appreciate the help

 

The seam on the firewall leaks. There was a issue with assembly factory work instructions. One side of truck instructions said to seal this seam while the other side missed this step.

 

When I bought my truck I removed all the interior and replaced it, the rear factory window on the area where the trim that runs along the roof channels was letting water in. I later removed those as they were peeling and went ahead and sealed those roof channels. NO JOKE a plastic razor blade made a tiny pin hole later on that roof channel and made a leak too super soft...... my truck is black and free of leaks I used permatex on the rear window looks clean and for roof channels 3M Marine sealant very happy with my result. But yeah those were my two spots water was getting in

 

Is this something I'd have to remove the window for or could I seal the window from the exterior? I feel like I know the answer but never hurts to ask. Additionally, is it terribly difficult to remove the rear window to place a bread behind it? I've got the same issue with the peeling roof channels and everything (channel really, one was already missing when I got this truck).