Re: high speed shimmy?
If you only feel it in the steering wheel, your probably right about it being the front. You might be able to see/hear something by jacking up one side at a time and spinning the wheel. If the pad makes more contact with the rotor in one place than the rest it's warped/defective. You might just want to cut your losses and contact the seller as Scott suggested.
White 05 WK 5.7 Limited
Added: REC Nav w/ In Motion Hack, Sirius, iPod | Mopar CAI | Hardwired V1