G540 + EMC2 = missing steps

if the axis is still slipping then , you still have not tuned the steppers correctly , so recheck your
stepper timings for the geko drives .

i'll admit i have not used the geko drives , as they are not so common here in the UK , but they are good , so see if you can find some settings that other have used , i dont know what the maximum voltage the geko drives can take , but increasing the voltage will give you speed , but it may be with all the drives running you cannot supply the current , so check your wiring , the thicker the wires the more current they can handle , and subsequently will hole the voltage better .

look at the spec of the geko and work out the max current and voltage , remember they use more current when holding position so for example and a quick way of knowing is if each winding = 2.5a thats 5.0a per motor x 4 motors = 20A
you say your using 12A so your only 50% there . ok it's a crude way and a quick way of working out what you need , so you may end up with 2 power supplys for 4 motors . without getting into ohms law and other peculiaritys

hope it helps .

Thanks for the thoughts!
The G540 driver is rated for 50v 3.5A per motor and lists a dissipation of 1.3A (68w)
Stepper Motors were listed as NEMA 23: Max Torque 282 oz-in, 3A
PS is 12.5A 48v
If the 3A is motor overall I should make it 10.3 A for 3 motors+dissipation. 4 motors is over the line.