My GM auto transmission did not like Dexron VI
This was my third drain and fill. The first one was done with original ATF - Texaco ETL 8072B, second and third ones with Castrol Dex 6. I went with Dex 6 because that's what BMW now recommends for GM hydromatic transmissions.
The result is not so good. The car now is sluggish, with slow, soft, long shifts. It feels like something is holding it back, as if climbing up the hill. No slipping , but does not feel right at all. Not good.
The level is fine, I'm an expert at doing this by now having done it 3 times.
I'm planning to drain and fill again with different ATF.
Just a warning - be careful what you put in your AT.