I'm sold on lining the truck with radiant barrier.
My ac is freezing cold, but with black on black, you can still feel the heat.
So far I've only done the back half floor and sides, but noticed a difference in heat and sound before I even finished that part(worked wonders on my garage doors and attic ceiling as well, my light bill literally cut in half).
Front floor/trans tunnel, and above headliner is next.