Car Stalled on Tranny Engagement

Patch's said:

I still think it’s the oil!
What I am assuming is that the engine is in proper working order.
You have just had an oil change done on the transmission. You have found that this has improved the performance in general.
However when it is extremely cold the engine stalls when you engage the transmission; BUT when the vehicle is at operating temp there appears to be no issues. Is that right?

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That's right. Thanks for the detailed explanation below. I tend to agree with you.

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Patch's said:

That is what I think is happening, though the cause is different, for one the oil wasn't changed often enough, sludge built up in the valve body, slowing or stalling flow regulation and or path.
Hot oil achieves a better working viscosity; that coupled with the hot valve body mass, things actuate closer to design. I think that if you keep up with the oil changes and perhaps drop some and replace more when the color starts to change, likely you will get ahead of it, or drop the valve body and clean it....

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Well, this is the second tranny service since factory fill. The first one happened at just over 80K, so in my estimation, I don't think it is lack of maintenance. Same guy does mine and he also does my ML and BMW - ex MB master tech, does only MB and BMW. We have talked sludge regarding the MB/BMW so called lifetime tranny, so he keeps an eye on it for me. This time, he says fluid was clean coming out, no metal filings, nothing unusual. When I did my 325i last year, he said some bad things about the tranny fluid he drained. On my bill, I see QTY=4 for fluid purchased - I assume that is 4 qrts of tranny fluid purchased, and supposedly put in 4 qrts? In any case, it was just as cold this morning but all went well. It very well could still be sludge, I'll keep an eye on it. Again, thanks for the detailed response.