Hello @EddieV ,
This is not out of the ordinary. ZBrush is a demanding application that will greedily use all the system resources it can get its hands on if it thinks it can use them. You can max out CPU usage doing nothing more than navigating with a fairly low resolution model if you continuously move the model around the viewport at length. This is especially true of meshes at a single level of resolution with no lower level of subdivision for ZBrush to substitute during the navigation process.
Remember that ZBrush is CPU-based, and does not offload any performance burden to the GPU in most situations. Your CPU will be doing all the work redrawing the canvas as you update it.
If you think you’re experiencing an issue that is not explained by the above, please contact ZBrush Support. Technical support for ZBrush cannot be provided over the community forums.
Thank you!