There’s little reason to ever deactivate local transformation under most circumstances. While it is active, the camera will pivot around the last point on the model you made contact with. What you’re describing to me sounds like what happens when the camera is not centered on the last point of contact, and instead rotating around either the tool’s center, or perhaps a point near , but not centered on your point of focus. This has the effect of making things feel like they’re zooming around wildly, because the parts of the mesh further away from the pivot move much faster when navigating.
There could also be other things at work.
Check the size of your mesh in Tool > Geometry> Size. The optimal size for working in ZBrush is an XYZ size of 2. This video explains some of the reasons why. If your mesh is significantly smaller or larger than this value, you could start to see odd behavior. In this case, use Unify on your mesh as in the video to resize and center the mesh for best Zbrush performance.
As far as the wild zooming, does this happen with a tablet, a mouse, or both? If it happens on a tablet but not a mouse, there could be a number of issues with your tablet.
You could also try enabling right click navigation for Zbrush. It may be a better fit for you if the standard nav is difficult for you to use.