[JRTJH]

For what it's worth, I live in northern Michigan where the winter temps regularly drop to below zero. It's not unusual to have 2 or 3 weeks each January-February where the temperature doesn't get above zero and -15F is a regular nightly occurance. I'm fortunate to have a garage for my truck, so I have never had a problem with diesel fuel. I also have a diesel farm tractor that I use regularly in the winter to move snow. It is stored in an unheated pole barn and I've also never had a problem with diesel fuel in the tractor. Both of my brothers in law also have diesel trucks. One is a 2010 F350 6.4L and one is a 2014 GMC 6.6L (I think) diesel. Neither of them have space in their garage for their truck and they've never had an issue with diesel fuel.

So, from my limited experience and those that I personally know, in the past 8 years, there's been no problem with cold weather operation, other than the fact that it seems to take "FOREVER" for the truck to warm up enough to provide cabin heat. The electric supplemental cabin heater that's optional on Ford diesels is a "must have" for cold weather living. I'm not sure if GM or RAM even offer the option, so.......

My suggestion would be that if you do buy a diesel, be aware of where you buy your fuel and keep the water separator functional by draining it as indicated by the owner's manual.