Well, there are some weird software interactions between the trans and the transfer case - maybe that was the cause in your case?

The ZF 6HP26 is used in many cars that dont have all-wheel drive (so no transfer case) and the 2-1 slam is an issue in these cars too...

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Wayne
2005 BMW X5 3.0d (b 02/05)
2001 BMW F650GS Dakar (b 06/01)