Hi,
The PE curve looks quite normal and with +-7.5" PE you are in the normal range of this mounts.
How much unbalance ? Not more then 250g (~1/2 pound)
How do you know that you have too much imbalance ? Touch the motor and if you feel comfortable with the temperature of the motor then it is OK, if you think it is hot, then back off with the imbalance.
If you have the brass worm then I would recommend to swap RA and DEC cables, take off the DEC axis assembly and let the RA axis run in for about 2-3 hours in every direction. This laps the worm against the aluminum gear a bit and the RA tracking could become smoother. Be sure to check the temperature of the motor all the time. Brass is by far softer then the used Aluminum.
If you put the Gemini tracking speed into terrestrial then you will not get a Stalled message for the RA axis if you do not have a motor plugged on it. Remember you are using DEC controller for the RA axis. ¿ Why ? because then you do not need take care of the slewing limits
Your guiding curve, I assume the values are arcseconds, then what you see is maybe the seeing what you try to chase
If those values are pixels then you are guiding above your image scale. Have you dome some imaging ? Perhaps as the RA values are the same as DEC values you will get round stars, because the RA and DEC movement are equal and it avergaes out.
I always use as guide speed 0.8x, 500ms exposure time. Try using the default values of PHD until you get a feeling. Then you can start adjusting the values downwards.
Also open the graph in PHD and watch the behaviour of the RA/DEC axis movement. That should give you also a feeling of the behaviour of your mount.