I ordered the 5-speed OD Auto trans also. I haven't heard many complaints other than the annoying drive-by-wire throttle delay. I have had experiences with automatic transmissions where the car would rev up by not move (accelerate) quickly. 99% of the time this only happened when the engine was cold (i.e. just started up). Once the car warmed up this symptom usually went away.
Is your transmission fluid level correct? Did you service the trans or change the fluid recently? You might as well have the car looked at while it's under warranty. If it happens again, drive the car for a while and see if the problem goes away.
This may be due to improperly adjusted bands or clutch plates which only "bind" well when hot (expanded). Same symptom can occur with older cars when the clutch or bands become worn.
Goto
www.howstuffworks.com and read the article on automatic transmissions. It's really interesting how these things work. $1000 extra seems like a deal after you read the article.
BTW, the 5spd Auto is the same one used for the GT ... so it's supposedly pretty tough.