Slow speed with stepping motor
I had a project where I needed to run two steppers at the same time as they were moving a heavy load and were moving the same piece.

While a servo is going to move the desired spot, a stepper will not.

In the process of setting up the stepper you designated steps per rev and amount of steps to take at a time.

The stepper is only going to move the "amount of steps" at a time for each run of the code. I ran into a similar  problem and I had to put in a 2ms delay after the servo run command to make the motors run smoother and faster, other wise it sounded like a bunch of gears gnashing and skipping.  These steppers were facing each other that is why they move opposite directions.


if (down==true){
  TLstep.step(-step1);
  TRstep.step(step1);
  delay(2);
}


I know it been a year since this was looked at. Hope you got your issue figured out.