How often should i change the oil in 2005 mustang v6?

If you have the "Timer" function in your car, reset it when you change the oil. It will run as long as the car is running. Then change the oil when it hits 80 hours. This will take care of changes between highway mileage (which is low stress) and stop and go traffic (which is higher stress and doesn't move the odometer as much)

If you don't have a Timer, just change it every 3-5,000 miles. Cheap insurance, and if you are a real cheapskate you could switch filters every other time, but it is best to just go ahead and change them.

Another thing people forget is to blow out the air filter as well.