The issue with engine oil is that water gets in it as a biproduct of combustion. So, oil must be hot enough to boil that water out. That temp doesn’t necessarily need to be above boiling at the sensor since oil touches hot items (pistons, turbos, etc) and will get the water boiled out that way. Transmissions don’t have that issue. I’ve not seen a spec on a min trans temp, but I think so long as it’s above 100F it’s fine. My Allison in the bus behaves the same at all temperatures until it gets too hot, then I’ll notice in the shifts. Since doing the cooling modifications to it, it’s been under perfect control and no issues. My engine oil cooler upgrades will require a bit more work but are working well. Today involved driving on Arizona 77 which is quite mountainous and lots of hard climbs. The cooling all worked great.