ANYONE KNOW WHERE PLUGGED DRAINS MIGHT BE LOCATED.

Under the hood, Passenger's side, at the very bottom of the black plastic Evaporator case. It's likely that all you will find is a short black plastic nipple sticking out of the firewall. Not easily visible but likely the cause of your problem. You'll probably have to get under the truck to find it. Might be able to access it from the right front wheel well but I'm not sure. Careful when you clear it not to puncture the Evaporator or heater core. You don't nee to go very far to clear it.

You might want to just blow some air in there. That is safer than running a wire in the drain hole.