“Can you step slice by slice if you use arrow keys or mouse scroll wheel…”
Yes! This is the answer! I figured it was something as simple as that.
On the Mac the arrow keys step 1 pixel over. As does scrolling, which
on my trackpad is set as a two-finger swipe up or down.
So I am in business. Just FYI, this is not medical imaging, it is geophysical.
I loaded the data from 181 slices as png images. The volume appears to
be constructed properly. Thanks for the help and I am excited to be part
of the Slicer community!