Prius steering shudder in cold weather and bad muffler noise

When you went to the dealer, did they drive the car and experience the shuttering? If not, I would take it back to them (or to an independent shop) and check your vehicle. If you really hit the pothole hard, it is possible you bent a rim, screwed up the alignment, bent a tie rod, etc etc. You could also have a very lose exhaust system.