how strict are your emissions regs?
dynomax has a nice long tube setup, they replace the cats too. its a set of long tube headers and dual cats that bolt right to the stock y pipe. i was gonna get these for my truck (but then saw theyre illegal in california emission regulated states).
dont waste your time with short tube headers (from what ive heard, ive never done any of this myself, i only know what i have seen/heard from others).
i think you might have more luck at this website with tech stuff with your truck, its another forum like this but all the posters are gm truck owners: