Hi Terry,
The settings look correct.
If you slew from one star to another and then back again, does it end up in the same place? If so, it could be as simple as a mount alignment issue that can be corrected by EQMODs N-Star alignment.
Also when doing sidereal tracking, does it follow a star? You could also try this during the day by timing one revolution of the worm - should in your case be 86164.0905/180 = 478.7 seconds. That would mean watching the mount spin slowly over the course of 8 minutes.
If however it doesn't get back to the same place, it is most likely an issue with the stepper motor skipping steps. This could be because the current setting isn't properly adjusted, or could be that you are slewing too fast for the torque rating of the motors. You could try slewing slow (setting the GoTo Rate to a lower value) and see if accuracy returns.