I posted this before, but if you really want to kill road noise from the back wall, hanging 1 piece of Mass Loaded Vinyl (MLV) the size of the wall will knock it down by about 20-40%. You'll want one large continuous piece and for best results hanging somewhat loose. It's actually pretty easy to do on the Ram. Just cut to size, then cut a couple slits where the seat belt hooks are. Cut a couple more from the retaining clips. Then hang it on and fit the rear liner back on.
I've played around with a number of different products to try to reduce interior noise, and MLV is by far the most effective to diffuse/absorb that road and wind frequencies.
Lots of info online about it. My personal unscientific trials consisted of running a white noise generator on my phone. Then covering it with various materials. Open cell foam did nothing. Closed cell foam did very little. Blankets very little. Butyl rubber damping material (dynamat) did very little (it does other things though). MLV.... Almost eliminated it. It's not super cheap and it's heavy, but it works.
In my last truck I lined almost the entire thing including door panels with Dynamat, Closed cell foam, and MLV. The truck was almost dead silent at under 35 mph. Then you go up against the window noise and nothing you can do. Only problem though was then you heard every other squeak and tick. And your kids..... Lol.