This is a very common issue with these little lathes. You will have to either loosen up some of your parts, take lighter cuts, or upgrade the motor controller. I think the first two options will get you fast results.
I did convert a 7/12 to cnc, but then I had to build another from scratch to get the results I wanted.
It is a much better machine if you can use it in full manual mode without threading though.
I did get mine to cut decent threads, but very light cuts were needed.
Also a very watchful eye and hand coordination on that stop switch.
Best to hit the estop at the end of the thread rather than trying to use the pot.