Scott,

The sorghums ahead of corn can be bad, but it depends on many factors.  Removing the residue helps (baling, etc).  Killing the sorghum before it produces lots of regrowth after the cutting will also help. If the sorghum-sudan is in rows, plant the following corn between the old rows to avoid the residue, to the extent possible.  Of course, killing the sorghum early defeats some of your reasons for growing it (all the more reason to choose some other rotational sequence in the future).

Do whatever else you can to prevent stress on the following corn crop.  Make sure you've got the necessary fertility in the right place at the right time, don't plant too early, use high-vigor seed, etc., and you can 'get away' with corn following sorghum.  Still not a great practice, though.