Being an electronics tech, I naturally gravitate to circuit failure. If I had to put money on it, my bet would be that the thermistor that senses the temperature of the seat is faulty. Perhaps FCA got a bad batch, and the reason that the heated/cooled seats work better is probably because they have a different model thermistor that detects both heat & cold. I recall reading that someone on this thread had a new seat put in and had the same results, but who's to say that there aren't other bad sensors out there that have been installed in both trucks and spare seats and he just got (un)lucky and his new seat had one of the bad ones. You, yourself saw this in another truck on the lot and other's have reported similar issues in their trucks.
In regards to firmware, one other member had the problem it move to the other seat. I don't recall if that was in addition to the driver's seat or just moved and magically the driver's seat started working. If in addition, it would be easy to assume that the second thermistor failed as well, if it just moved, well that's a little harder to explain..... Either way, unless someone got into his PCM and changed the firmware, I can't see the passenger seat start failing (after previously working fine) because of a programming issue. It seems to me that it would have always been bad.
Just my 2 cents.