I want to change my transmission fluid and I am not sure which of the two use. I have used pennzoil synchromesh in the past on an 04 gt I had it held up well. I have read several threads on the subject but have yet to find out which of the two is better to run and if Amsoil synchromesh is safe to run in the 3650 or not. Is anyone running Amsoil's synchromesh or GM's that can reply back.