A tune from a reputable tuner like Bamachips or Brainspeed can get the horsepower and torque to within 95% of a custom tune. Good enough for a daily driver. It also increased my MPG with both city and highway driving. It will greatly improve throttle response and auto trans shifting. A dealer can deny a claim if a mod is the cause of a problem. There is no such thing as voiding a warranty. Some people on this forum have claimed a warranty can be voided if you don`t keep receipts for oil changes. With the proper procedure, I can reinstall the stock tune to my car for any mandated PCM updates from the dealer and go back to my performance tune without the tuner getting "unmarried".