Hi @arten,
Try this:
pathslope.gh (188.3 KB)
The approach I used is this - dividing a straight line between the points into many segments, then fixing the ends of these segments in Z, and controlling their length.
If they all have the same length they have the same slope, because the difference in heights of their ends is equal.
The points are all pulled onto the target landscape, and there is some bending resistance to make the corners smooth.
Obviously you cant have rounded corners at the hairpin bends while staying exactly on the landscape and also keeping exactly the same slope. You can play with the relative bend/pull/length strengths to control this.