Does a headliner make a big difference acoustically?

[AirSpeed]

My 72 GMC 4X4 is quiet inside as far as wind and mechanical noise but it doesnt have the "dead" sound I want, I am thinking about putting in a headliner to deaden the cab. I have 3/8" thick rubber mat glued to every surface, the entire floor, behind the gas tank and on the gas tank. I have acoustic foam on top of the rubber mat on the gas tank, foil faced acoustic mat under the carpet plus the pad that came with the new carpet and it still isn't as dead inside as I want. I have never been in one with a headliner so I have no idea how big a difference it will make. I like the way it looks painted so I dont want to cover it up unless it's going to make a big difference.
Have any of you noticed a big improvement with a headliner installed? I am also wondering if the chrome trim is necessary to hold the headliner up? Can the headliner be used without the trim?
Thanks for any help! Aaron