I dont really understand. Did you get them from the dealer? Maybe they sold you the wrong year or for the wrong truck? 
Unfortunatly the GMC and silverado lower valances are different. I think the GMC fogs mount from the top as well though. Maby ask admin ob1_jr. He hs a GMCI bought it off a guy that had it on an 07 GMC. Not sure if it had fogs or not. I was just wondering if the rectangle lights mounted a differant way. If not it is time for a little moddin. It bolted right up so it is for the rite truck, just wonderin about the fogs.