It is transmission fluid, not engine oil, in the coolant. They have been in touch with tech support and are working down their list. They called tech support since it is a first for that shop.
My truck has oil in the coolant reservoir. 2020 Silverado 2500HD Z71 WT with 6.6L gas engine, 9,300 miles. I am still waiting for the diagnosis from the dealership. Has anyone experienced this issue in a new truck? Update, the transmission cooler in the radiator failed, replacing radiator and hoses, everything that is saturated in transmission fluid.