Randy,
Throw in a picture and your G-code or settings and material information. The more information, the higher the chance is for a competent answer 
This can be stepover as you mention, and it can also be related to the tramming of your spindle. (if the spindle is perpendicular to X & Y) if its not, it will be cutting on a “edge” of the bit and this will leave a noticeable mark on your surface.
Are the finish you describe a result of a light finishing pass? Or are the marks left in the pocket after a pocketing operation? If this is after a pocketing operation it can also be a result of deflection.
Do a finishing pass in the pocket with <90% stepover and a low depth of cut, ensure that the DOC is enough to remove the “old fun”. If there are still marks, this will indicate that your router/spindle needs to be aligned on X & Y axis.
There are several posts on this forum and on google/youtube on the tramming subject.
Edit: In the ebook there is also an enourmous amount of usefull information