Ahh crap, I just purchased some kooks long tubes for my 06. Now according to kooks the headers for 05 and 06 are the same but I think the y pipe is different. Would you provide more specific details as to why the headers don't fit? Is it possible you have 4wd headers for a 2wd or vice versa?
With the edelbrocks you are not supposed to move your cat, apparently 06 models have cats closer to the manifold. I even phoned edelbrock myself, and they gave me a new part number for 06 trucks, but no one has any stock on them yet. Also in 06 there is a difference between independent and solid front axles, edelbrock only has headers for the independent front.