So, on my way home last night my CEL came on. I read the code this morning: P0430 Catalyst efficiency below threshold Bank 2. Arggh. Fortunately, the shop is pretty sure it's their fault and they'll fix it for free on Tuesday. It's probably a leak from a bad weld or a pinched O2 sensor wire.

05 WK 5.7L
K&N 57 series CAI
True dual Flowmaster exhaust