Oh dear, it looks like all the text were dropped when I attached the two files and hit POST.
1. Source of data:
I downloaded the example file Florida_palette_hill_shading.map from Manifold Release 9 downloads and examples files. I exported the Florida image as GeoTIFF for Manifold 8 (Build 220.127.116.11).
2. Creating slope surface in M8:
I imported the Florida GeoTIFF,
EDIT>SAVE MASK/CHANNEL (Save: Surface: slope) To: Slope Image
I then opened the Slope Image and VIEW>DISPLAY OPTIONS and selected CB RdYGn 7 (reversed) palette, and set the "Height" values at 0, 2, 6, 12, 20, 25, 45 degrees (to correspond the the local slope classifications for Flat, Undulating, Rolling, Hilly, Steep, and Very Steep respectively). The image was exported in the layout with explanatory captions.
3. Creating slope surface with M9 (Build 18.104.22.168)
With Florida image open, TRANSFORM>SLOPE (radius 1)>Add Component to create Florida Table Slope Image
Open Florida Table Slope Image, STYLE>Channel 0>7 Breaks and chose breaks at 0, 2, 6, 12, 20, 25, 45 degrees and palette Green-Orange (the closest I can find and which is reproducible) to correspond to the M8 display style, and exported as a Layout.
The point I'm making is in M8 the slope classes are mostly in the greens and yellow (0-12 degree), while in M9 there is a significant level of orange (>12 degrees). I have tried transforming the slope images to contour areas and in M8 the 0-20 degree range totaled 99.9% of the total area while in M9 it was only 44.5%. I have also tried out the slope transformation with the raster in other example files from the same source, and they all show a higher reading for slopes in M9 compared to M8.
Another interesting observation I made was that the slope image from M9 appears to show edge artifacts - there is a distinct appearance of 6 tiles in the image while the slope image from M8 was smooth.
I hope there is now sufficient information for others to test and advise if I made a mistake somewhere.