Lack of Torque, Missing Steps

I'm looking for a bit of help on my motor setup. I have a hand built CNC simialr(ish) to the Gatton Sidewinder (40*26).

I spec'd the motors and driver myself but I'm beginning to think I've made some pretty major mistakes when choosing. The machine doesn't have very much torque and on some test runs (cutting birch ply) it's missing steps. I'm running a two flute 1/4" downcut bit with a bosch colt router and doing 1/32" cuts at 39in/min and still missing steps as the peices are slightly off on measure and are not square.

Here is the current setup:

Stepper Motors (1x Z-Axis, 1x Y-Axis, 2x X-Axis)
Model: 23HS9430B
Pahse: 2
Voltage: 4.8V
Current: 3.0A/Phase
Inductance: 6.8 mH/Phase
Holding Torque: 280N.cm Min
Detent Torque: 12N.cm Max
Rotor Torque: 800g.cm2

Driver
Model: Geko G540
Also I have a 3K ohm resistor wired at the driver connection for each motor. I forget where I read that this was required?

Power Supply
Model: S-600-48
Output: 48V 12.5A 600W

Lead Screws:
1/2-10 RH ACME Rod, 5 Start

This post has me especially worried: https://www.cnczone.com/forums/diy-c...25720-cnc.html
Excerpt: "I see a lot of people buying the wrong motors because they think that 425 is better than 387. Larger steppers suck at higher rpm's and have high inductance, which means a large expensive power supply to drive them."

At this point I'm just trying to cut a new gantry for the machine using the current machine without missing steps, I'm not concerned with speed.

My initial thought was...
Combined Motor Voltage 4.8*4 = 19.2
Combined Amp Draw = 3.0*4 = 12

But now I'm seeing that I missed out on the whole inductance thing...

The G540 max voltage is 50 so, I'm up against the max for voltage already.

I can buy new motors or a new power supply but, I'm just not sure what's best here. Humbly asking for any feedback or help you may have to offer to help me get this thing up and running.

Would smaller motors help get me more torque and work with my current driver/power supply?