One other place to apply an acoustic mat is on the roof of the cap…I have a 1/2” thick peel and stick pad that I got from dynamat (I think) that I installed on the inside roof panel, and then installed the cardboard headliner over it. My cab is very quiet- but I also have dynamat over the entire floor, under the seat, along the back wall below the rear window, and up the front firewall.. also, some applied inside the doors. I think he doors and the roof stops them from drumming…whatever it is, it worked really well.
