I have a 2000 Mustang V6. I recently installed had a shop install a custom exhaust and today a Cold Air intake. I did these upgrades for the sound, better gas mileage, and a little more hp. a) The exhaust consists of a Flowmaster series 10 muffler and the addition of another pipe for a "dual exhaust". On first gear, it almost feels like the car lost power when you start moving. It's like it has low back pressure. I don't really notice any HP gain, and gas mileage seemed to actually get a little worse. The sound is good though. b) I had the CAI installed today (K&N Cold Air Intake) and I have a number of issues. First of all, the check engine light is on all the time now. The car seems to jerk a little when you let the clutch go. Overall, I feel like both upgrades were a waste of money. I don't see any gains other than the sound. If anything, the performance seems to have dropped. Was something done wrong? Any ideas or suggestions? I had the car tuned-up about a month ago.