Both my cases and my trans shift smooth as silk.  There was no break in period or anything.  Something must be wrong internally or there is some inter ferance issues with the sheet metal, carpet, shift boot??  I had to trim my shift boot.  It kept popping out of 4lo.  This was due to having a body lift and the boot being all bunched up and tight.  I almost always have to push the clutch in to shift the cases.  They shift the best when rolling slow for me.  Hope some of these ideas help.