Originally Posted by coppertone
I had it done against my knowledge by the dealer and my car felt like a slug afterwards.
That's because the ECU was reset and it needed to re-learn your driving style and typical throttle inputs. Whenever the dealer resets the ECU, always drive it like you're possessed for first 20 miles after reset, and it will adjust to you.
Depending on your State, you may be required to have this service done in order for you to register your car this year. This was the case with my 2012 LGT when the WQC-39 came out. The State was notified because this was emissions related, and I would not have been able to register the car again in July if this had not been performed.