Trans shifting hard
 

Took my '08 to the dealer today. Has a rattle under the hood, and a bad weather seal on the driver's side rear door, but also an annoying intermittent problem with its shifting. Most times it is fine, but about 6 times (in 7000 miles) the auto trans has started shifting extremely hard. Not firm like when its in "I", but like neck-snapping, slam-bam hard (well, as hard as the 2.2 can muster). If you pull over, shut off the car and restart, it goes away. It usually happens while driving after stopping at a light, but did it once right after initial start up.
Of course it hasn't done it for the tech, and the computer tells them everything is fine. I know problems like this can be hard to find, so I'm hoping someone here may have had experience with a similar problem.
We previously had a '99 Chevy Venture which did a similar thing and I was told it is a common problem with a solenoid in the trans on those vehicles. Inexpensive part but mucho labor to pull the trans and install it. That one started after it had 100k miles so we never bothered to fix it. Almost 190k on it now and still going strong. But the trans problem was one of the reasons we bought the new car, so we are anxious to get this one taken care of.
Hoping to hear some good news here.

Update
 

So we really got nowhere with the last visit to the dealer with this issue as it would not repeat for them. The rattling noise went away, even though they claim they did nothing to it!
The trans did repeat the hard shifting a couple more times for us. Then on Tuesday morning it felt kinda funny when shifting while on the way to work, but not as harsh as it was before. After work, however, my CEL was on when I started it. Called Onstar for a diagnostic check and they told me there was a code for the transmission control circuit and to bring it to the dealer within the next day. :cool: Trans was shifting fine at that time.
Turns out to be a P0717 code. Slip says low voltage to Speed Input Sensor. They tore the trans out and replaced that and a wire harness and some other parts. Hope this fixed our trans problems!

That hard shifting must be some kind of default because the same thing happened to mine when I forgot to plug the MAF back in after checking the air filter.:red: