As I understand a tune allows an EFI to be reprogrammed and have timing adjusted and fuel remapped [like rejeting carbs]. The Tuneboy has the added benefits of correcting the factory speedometer error, removing the factory timing retard in 1,2,3, gears, allows the secondary butterflies to open fully, and removes the factory top speed limiter. As opposed to a Power Commander witch will only adjust air fuel ratios to help compensate for intake / exhaust changes If I am mistaken I'm sure someone will correct me soon.