sblantipodi wrote:it all happen in the same loop,
Lets see some code, since something tells me you're not using an interrupt or you're just doing things wrong.
You need to create a timed interrupt for the stepper motor only, not both (you put the text in the normal loop).
Another possible option could be creating a state machine.
When you're new, don't start with a separate ESP (ESP-01 to ESP-14) module.
Get yourself a proper development board: NodeMCU - WeMos D1 - WeMos (UNO form factor) - Witty Board
ESP power requirements are 3.3V±10%@350mA
The ESP8266 IS NOT 5V tolerant on ANY pin (see item 5.14 on page 25 of the FAQ)