Please see this link to see a fine example of what I am dealing with.
My specific situation is that I have downloaded DEM data from the National Map (USA) and it comes in GCS North American 1983 with no linear unit. Without a linear unit you cannot calculate slope, so in order to calculate the slope I project the data in the appropriate UTM zone (using both ArcGIS 10.4 and ArcGIS 10.2, Project Raster tool) and what I get is a DEM that looks like it was made of clay and someone smashed it up against a chain link fence (just like the examples in the aforementioned link).
I see that the linked question above was closed for not being specific enough, but nobody really provided any kind of answer either, and to me the question seemed pretty clear. Maybe we are both going about this the wrong way, is there a better way to project a raster or assign a linear unit to a GCS dataset?
I would use a different dataset, but there really isn't one and I feel like this data should be usable since it is the National Elevation Dataset.