Found where the leak is coming from. The cabin pressure relief vent below the rear window on the drivers side. Ordered a new one. Will be here tomorrow. Now just to see how to change it out.
2019 gmc sierra 2500hd. Just discovered my back window was leaking. Went to get in my truck and squish. The whole floor board is saturated. I'm just outside my warranty so who can I contact to have it fixed.