Hello @mpormon -
What is the resolution of your DEM? And how large is your study area? If the cell size is very small, and/or the study area is very large, it can take a long time.
If this is not the problem, then maybe there’s something funky about the DEM itself, in which case it would be helpful if you would post your entire datastack so we can try to run SDR with your data. Please see this post for how to create a datastack. Thanks!
~ Stacie