Battery voltage is definitely an issue when programming in cold weather, but according to Ford's own internal documents as well as documentation from the manufacturers of some of the components, the PCM should not be reflashed until the unit temperature is at least 35º F (3º C). This actually has to do with the way the flash memory is written, which can be unstable in colder temperatures.
The best solution, as Jack indicated, is to run the truck for a bit and allow it to reach full operating temperature. This gives the battery a chance to receive a full charge and allows the PCM to warm up internally. Also, as Jack so wisely indicated, makes sure to turn off any accessories such as the heater blower, DRLs, and radio.
One thing people also overlook is the impact PTT (Nextel) Cellphones can have on the communications. CAN is a very robust communications protocol, but the microwave emissions to and from the phone can conceivably cause an issue during programming so I'd recommend keeping it far away from the programmer. I'm not aware of any specific instance where a failure occurred, but better safe than sorry.
Thanks for catching that one, Jack!
Oh... and 3º F. is freaking COLD! Brrrrrr!!!
Hope this helps.
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