I took my IS220D back to the Lexus dealer late last year they said it was a common problem and said they had a 'fix' for it. It was ok for a couple of months then it happened 4 times in about 20 minutes one of them while overtaking, so back into Lexus they took it for a test drive and found no problems, so they changed the gear box oil ??? It has been ok since last week but the next time it happens I agree with the other post is to demand a replacement gearbox as I am expecting to keep the car for a few years, I have done 10,000 miles now 18 months old.