I'm pretty new to the Arc Hydro Toolbox.
I used assign stream slope in the Arc Hydro toolbox. It produced a mostly correct to and from elevation. However, if you look at the purple arrow, it shows a mistake. That river goes from low elevation to high and then back down to low (the highlighted main river channel is low again). It does it again at other locations above the purple circle.
Any suggestions on how to fix this? Are there any issues with a river line file that could trip up the tool?