Try getting your wheels rebalanced, check the pressure too, even them out atleast side to side, front to back isnt really an issue. If that doesnt work it may be time for an alignement. i've also heard warped rotors can cause vibration, but i can never figure out how unless you're braking. Any uneven wear on your tires? *edit after reading other shaking post* Torque all your lugnuts, if you havent since the shop put the wheels on, they probably arent torqued evenly.
Just curious, anybody know if there's anything in the steering system that can slacken up? tie-rods and the like?
The one time i had my car over 200 it was rock solid.