Changing graded quiz points

To use multiple sliders on a graded question slide, you need to disguise a standard question slide. For example, you could put your custom question-with-slider info on top of a T/F question (i.e., hide the True and False buttons).

Then, instead of the triggers you currently have that show the Correct or Incorrect layer based on the slider values, make the triggers change the state of the True or False button to Selected. Be sure to put those triggers before the default "Submit True/False" trigger on the Submit button.

This post doesn't directly address your situation, but it does provide info about "disguised" questions:

https://community.articulate.com/discussions/articulate-storyline/tip-give-partial-credit-on-multiple-response-questions