check the power supply wiring, I would use 16 or even better 14 AWG between power supply and drivers and connect a capacitor 100nF and a elco 100uF close to each driver.
If the cables to the motors are long, I would also use 16 AWG for these and advise shielded. These steps will help in preventing interference between the axis. It will not solve the max speed you can reach. That's related to the motor inductance and the driver voltage. A lower inductance and / or a higher driver voltage will give a higher speed.