we got an arctic blast here in Texas and my e-420 also shifted roughly on the coldest morning, i was in Winter mode and it happened only once but the shift from 2 to 3 was strange.My 97 E420 with 158k on the odometer has issues shifting normally/smoothly when cold. Works fine when it warms up. By cold I mean Arizona cold not Green Bay cold. The shifting is a little jerky primarily for the 1-2 upshift and surges a bit until warm. I've started placing it in winter mode to avoid 1st until it warms up.
I am also wondering if the issue is maybe related to the e-throttle, but that is an electronic device and so doesn't warm up like the transmission does.
The fluid is correct and recent [less than 2k miles]. I haven't checked the level too recently though and plan to do that when I get home from work this evening. That's 18 miles traffic so it ought to be warmed up to 80c. I'll check the temp with my IR thermometer and see where it is level wise.
no problem whatsoever since then though...