Lexus issued a service bulletin for a hard shift condition from 2-1 when coming to a stop. That bulletin was issued in 2012, and it covered 2006 GS300 models (both RWD and AWD), and 2006-2007 model GS430s. Basically, the troubleshooting called for having a tech test drive to verify the condition, and if the condition was present, replace the ECM. No other troubleshooting steps were requested or required for this condition.

Here is the bulletin:

https://static.nhtsa.gov/odi/tsbs/20...61736-2273.pdf