Just In case, you dont after market wheels on it do you? If so are the lug nuts the right fit for that style of wheel. and just out of curiosity are the wheels centered up right on the hub and those little clips that hold the brake rotors and sometimes brake drums have when they come out of the factory. IF you do not remove those they will cause Vibrations and sometimes the wheel(s) to come off. I work at a tire shop and have pretty much seen it all, just throwing some ideas out to see if it helps. maybe you also have a bent wheel or 2? It doesnt take much bend to cause a wicked vibration. like Eric says stay basic then you can really narrow it down. Robbie