hmmm.. Thoughts and suggestions:

1) As stated in a previous post: The throttle automatically calibrates it self every key cycle.

2) Since this is drive by wire- there are no adjustments.

3) Since everything is computer controlled for EPA standards- there are no real adjustments. The transmission can be forced to relearn, and thats about it.

Now- I dont wish to sound mean spirited- only bring this up in fact, because someone on this forum actually had this happen to them:

Is it possible that your vehicle was left in the W or winter mode for the transmission? This provides different gear ratios in both forward and reverse, to reduce wheel spin in snow. Is it possible, they simply switched you back to S or summer mode? Someone on this forum did have this happen to them- and drove for quite some time without even realizing it! Quite the surprise when they figured out what that little W/S switch did!

Just my thoughts