the black material that surrounds the bed of my Chevy Avalanche

I see a lot of Avalanches with faded out plastics. Look at Meguiar's products and see what you can find. It can be made to look better but if you want it to look great you will need to replace all that plastic. You may be able to paint it to match the truck or a different color. Talk to a body shop.

If you get a small torch and go over it but not to close it gets it like new!