GM sent me a letter yesterday! First one for me and Dockman this might apply to you too. It seems there is a computer software upgrade for the transmission.
"The update that is being made available to you is voluntary and enhances shifting performance. That means you should expect smoother, more responsive shifts with this software update."
After the update they mention that it will take some time for the system to re-learn your driving habits and that your fuel economy may vary. Better or worse? It doesn't say.
Well I guess I'll wander down to the dealer and see what this is all about. I have not tried racing before but maybe I can after they 'flash it' - Yeah zero to 100 in 12 seconds would be much better that two minutes. Just kidding folks.

Actually it isn't bad now and the other day on the 401 I zipped up to 140 for a brief moment and scared myself - 50 over was close and too easy to get there - I'll have to behave.