RJDiesel,
I have a 03 Excursion with the 6.0L. I usually run a fuel conditioner / lubricator like Power Service Diesel Kleen the silver bottle in the summer and the white bottle in the winter. The white bottle had anti-gel additives to help prevent the diesel from gelling in cold temps. Being at 100k you are due for a coolant flush and replacement. I would stick with the gold coolant that is in there stock, which you can only get from Ford. It is a little pricy but it has the protection additives that your engine, and you don't have to worry about cross contamination. If you do not have verifiable maintenance records, I would look into replacing all the "life fluids" in the near future. The transmission fluid (Make sure to ONLY use the Mercon SP fluid) and if you do it yourself don't forget the remote filter on the right front frame rail near the bumper, change out the differential fluids and the engine oil. I would also replace both fuel filters just to have a good starting point. Also, grease the chassis..... Then for routine maintenance from here on out I would change the oil and filter every 5k miles and the fuel filters every 10k miles. The clean oil and fuel filters are important for the injection system since the injectors use high pressure engine oil to fire the fuel injectors. Then follow the owners manual for the recommened interval for the other service.
Could you be more specific on the temperature conserns you read about.
If you keep it stock, I have heard make no changes fom the Cat forward it should live a long happy life......