I would be very hesitant to use 20w50 in cold weather. GM always leaned toward thinner oils. Higher oil pressure is not always better. If a gasoline engine was completely rebuilt, running oils such as Rotella and Delo is ok but not needed. However if they have a lot of miles, these oils that were designed for Diesels, but approved for mixed service will dissolve buildup that you really don't want floating around on your system. By the way I sell Rotella and Delo both.
