Added -DX12 to the TSW Steam Launcher. Task manager showed that the GPU was not being utilised much, but the framerate was up and CPU usage down. A quick search on Google revealed that taskmanager does not report GPU usage properly when playing a DX12 game, and the recommendation is to use HWinfo instead.

HWinfo is a free download, and I can see that the GPU is running at 99% in DX12. I neeed to find a way to tweak HWinfo to be more user freindly. UPDATE - double click on the sensor to get a graph.

For task manager to display GPU usage, click on a GPU graph heading label and select Graphics_1