Is it vibrating when you brake or just when you are driving? It could be a warped brake rotor if the mechanices used an air impact wrench to put your tires on. But I still think it's tires/wheels. The new wheels could just be junk, I don't know how good loco products are. See if you can get another tire/rim combo on there. Borrow someone's wheels if you can, or if you have the old ones, put those on.

99 Silver SVT with:
lowered-eibach springs, piaa fog lights in upper mesh grill, K&N filter, tinted, flowmaster mufflers, straight-piped cat(temporarily w/ca. for emissions), custom spoiler