to cut down on noise, u will need 2 layers of dynamat on the headliner, one on the floor, plus u have to lay a thick foam pad over it to get it more quiet, u guys did fully deaden the doors right? inside one layer and then outside one layer? i used the mega bulk pack and that covered everything but headliner and floor, still need some more to finish the job, but now its good enough. also when u guys dynamat the tailgate one in and out, do not roll the window down and open it, itll fall back on u if u dont force it up completely.
I think that assertion may be a little strong. You don't necessarily need two layers of dynamat over each other to cut down on noise. It may cut down on more noise, but at some point you get smaller and smaller incremental gains...