Frame And Members problems of the 2006 Chevrolet Colorado

I own a 2006 Chevrolet Colorado with 14,000 miles on it. I have taken my truck to the dealer on at least 5 occasions complaining of a terrible vibration. The vibration is horrible from 40-55+ miles per hour. The dealer has so far replaced the 2 front tires, replaced the air inside the tires, rotated the tires and most recently stated there is nothing else they can do. After the last visit, I said there is something wrong with the truck and you or gm are going to have to step up and do something. This is my only transportation and I am very nervous about driving the truck with this terrible vibration. Please let me know what else I can do. I think a recall is in the cards, either to replace the all the tires or make modifications to the truck frame, etc.