550 v6 transmission not responding dead up hill

Hi the other day i was going up a hill and trans went dead. No lights nothing move selector into neutral and engine revs put into gear and nothing no kickback . I turned car off and started back up and works fine again this is the second time it has happened to me although its a bit slow to kickback going up steep hills normally have to pretty well put ya foot into it.

Anybody got any suggestions before i take it back for waranty pretty hard to diagnose cause hardly does it and does not bring up codes or log nothing

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Anybody had this issue

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Have thought on occasions that mine should have shifted down towing the van up steep ranges but it was still in the middle of the torque range so just let the box decide what to do