Look in the drivers side door sticker to see when the truck came off the assembly line. I believe anything after May 2004 should have the upgraded rotors and brake kit.
Just to verify, that does not mean purchasing your vehicle after May, it means that the actual production date was May of later. If you bought your truck in May, it probably was produced before May.
Of course that doesn't mean you will experience an ounce of problems, so I don't want anyone to think that's what I mean, just stating that the Brake fix kit's were applied to the may and post may vehicles coming off the production line.