| RE: Vibrations
While I wouldn't rule out other problems, it does sound like tires to me. There are tires out there, that no matter how much you balance them, they'll still shake or bounce a little.
You say they are Continental tires, but I haven't heard that much about them nor ever owned them. My dad had a set of Goodyears on his truck that did the same thing as you describe. He pulled them off and replaced them with Michelins. Problem was solved.
Very few tire manufacturers admit that their tires are bad but sometimes they do. I had a bad set of Dunlops one time, three of the four separated with less than 5000 miles on them. I had to threaten them with a lawyer before they would get right with me about them.
I personally don't think you'd ever go wrong with a set of Michelins. I have bought them for years and have never had a bad one. But it does happen.
I have a new set of Michelin Cross Terrains on mine. They are one sweet ride! | 
