To close this thread the temperature before turbo is a red herring - so the 849 degree is irrelevant. My DPF issues were down to an air leak on the inlet side so unmetered air was being drawn in so the fueling was off as the MAF would not detect this additional air. Found by smoke testing the inlet. After replacing all the gaskets in the vee, to solve oil/coolant leaks plus gasket / diaphragm on PCV the problem is solved for over 18 months now.