It sounds like images were acquired with anisotropic resolution. To confirm, choose Window/Information and look at the "Spacing" column for the Spatial dimensions, I suspect you will see that the image spacing is of higher resolution in plane (I Space, J Space) than the between slice resolution (K Space). If this is the case, this reflect properties of your image acquisition. Rather than acquire three orthogonal series (Coronal, Sagittal, Axial) with thick slices, I would suggest acquiring a single 3D image with isotropic resolution. I suspect this will give you similar SNR with similar or lower can time.

If this is the case, you might want to choose the option "Reorient images when loading" which will interpolate your data to isotropic. Alternatively, if you have a modern computer, I would suggest using MRIcroGL instead of MRIcron, which will stretch dimensions by default. Whichever method you use, images will exhibit poor resolution across slices, reflecting the inherent properties of your acquisition.