I also am planning a trip from the Black Hills back to WI. With all due respect to the OP, I am interested in knowing if Hwy 14 through MN is a good road with decent shoulders and what the traffic might look like.
I rode US14 east-to-west across Minnesota a few years ago. As I recall there was ample shoulder but the frost cracks were often a bit annoying. But that is probably a common problem in that part of the country.