Steve,

In the northeastern US, we pretty routinely fly in 25-35F in the wintertime, and I've never experienced decreased range in the cold (and I've been flying all JR for 20 years, from the 512 PCM to the current 12X).

The 12X is substantially more difficult to take apart due to the arrangement of the RF section. In the US, there have been some battery issues with the 12X, which could be magnified in the cold (as Tony F suggested), but since the TX output is regulated, I'd have expected the low voltage warning would go off before the range was affected. Good to hear you are getting it checked out.

Regards,

Dave Lockhart
Team Horizon/JR/Spektrum