One problem related to transmission slip out of gear has been reported for the 2006 Toyota Matrix. The most recently reported issues are listed below.
I have a 2006 Toyota Matrix and the vehicle started jerking when it shifted out of 1st gear. It jerked so hard that I had to be careful to not lose control of the vehicle. Also the vehicle would stall when I would be in heavy traffic. The shifting issue occurred every time I drove it after the problem started. The stalling issue occurred around 5-6 times when I was driving. I recently took it into the dealership and they replaced the ecm for a cost of over $700 since I was out of factory warranty. So far, the problem has been corrected however, I noticed a service bulletin in 2007 which I believe Toyota should have informed customer's. This was very scary when it occurred and luckily I didn't end up in an accident.