I live in northern ca and we get into the low temps and have had 0 issues and been running 3 years like this. I would rather my trans run cold than hot. The converter is still going to heat up the fluid a good amount and run fine. Anyone that runs compounds on their truck removes the heat exchanger.

 

I think 150° while towing is right in the cool-normal range

 

a lot of the head is how efficient the converter is. My original converter I had would run 170 towing on on some grades run 200 found out stator was cracked sent it to local shop they fixed it and same trips it runs 145 most of the day till stop and go traffic in town it gets up to 175-190 as soon as I get rolling it's back into the 150's and on long hwy runs will run about 125.