Originally Posted by m4a1mustang

Diff fluid is dependent upon how hard you drive the car. If you track it regularly... probably every track day, or at least every other.

On the street I'd say every 20-30k is fine. Some people go much, much longer with no issue, but as I said it's dependent on driving conditions.

Spark Plugs... those go a while. First scheduled plug change is 105,000 miles.