JoeNova:
For now I am using the built-in stepper library.
JoeNova:
...it will add/subtract 1 step via myStepper.step(1);
The problem is, the loop operates much faster than the stepper can react, so it quickly piles up the steps before the temperature hits the target, so the temperature overshoots the target,....
Have you read what I wrote above? If you use the built in library the loop does not operate much faster than the stepper because the step call will wait for the stepper to complete its step before going back to the loop...
So you have a logic or other type of bug in your code which you have not posted so can’t help....