The steppers all running at the same time use very little power. if I remember right 0.3A. Steppers aren’t always moving so they aren’t always using power, they step. 5A is more than enough by far.
Did you take the belts off?
If they move crappy and weak with the belts off you have them wired wrong.
Reply To: Steppers Stalling VERY easily/ No power or torque