One problem related to transmission slip out of gear has been reported for the 2008 Toyota Sienna. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2008 Toyota Sienna based on all problems reported for the 2008 Sienna.
The car was driven normally in gear "d" at 35 mph but slipped out of gear for no reason. I stopped, put in park, turn off the engine, waited a few minutes and restarted the car. It would then only work in gear "3" but I had to floor the gas pedal. After stopping multiple times, I was able to reach home. My 2008 Sienna can now be driven forward in reverse gear.