Haven't seen mice in our half tons, but both my dad's 2016 and my 2018 2500 have had mice get in through the cabin air filter. You need to pull the wiper cowl off and pry open the siliconed lid that's above the cabin air filter. Once you get that lid off, you'll see its wide open to the cabin air filter. We both found some wire mesh and siliconed it to the opening. Sealed everything back up and haven't had an issue since thankfully.