I've had the infamous wet passenger carpet/floor for awhile on my '05 Z71 and tried all of the other sources for leaks. After having the blower motor resistor/speed control (auto climate control) short out Thursday morning on the way to work, I took the cowl apart today to discover the seal around the outside air intake was basically done for. Water was coming in there and flowing down onto the resistor and blower motor then continuing onto the floor. It looked like it was coming from the firewall, but after finding the outside air inlet, that is the source of my problem.
There is one screw on each side of the cowl (under a flap to allow the hinge to open when the hood is raised) and four clips along the front of the cowl that hold it in place. Wipers having to be removed to get the cowl fully off, but will be doing that later this afternoon once the new resistor comes in to the dealership. This picture is what the "seal" looked like when I was finally able to get the cowl up.