I had somewhat similar issues but on my BMW X5 2005 4.4 with automatic transmission ZF 6hp26 at around 170K miles. I rebuilt it, completely refreshed the oil and it now shifts like new. I did all the work in my parking garage on my back
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https://xoutpost.com/bmw-sav-forums/...n-success.html
Go through the thread. Valuable info. I think it was an overkill to replace the mechatronic separator plate and damper pistons given no codes but only poor shifting and slips.