What year is your truck? I'm assuming you want painted fenders yes? if so then you could do that but a cheaper alternative would be to paint them yourself or have a shop do it for you. and welcome to the site.
They should be the same. All you gotta do is take care of the clips that hold onto the body and the fenders. As for the thickness I don't know. Why don't you line x your fenders. I don't know how well the plastic fenders hold up but if there like the Chevy Avalanches they don't last long and fade. However I did see a couple of old 4th gens, I'm guessing 03 04 at some of those junkyards off I35 if you wanna snag some.