@Alex_Wiebe twisted pairs. That is your highest rejection method.
Right now there are no extensions between the board and steppers. To implement twisted pairs, I will have to cut the current leads back to how close to the stepper and replacing with twisted pairs?
In general I’ve had success with chokes on a homemade CNC machine (causing sporadic steps) - how critical is it wrap the wires around the choke or is passing straight through once as good as its going to get?
Related - if I go with twisted pairs, is there any merit to using chokes in addition?
You don’t cut back the wires. You simply pop the pins out of the connector and start twisting.
The important piece is the uniform ness of the twists. In principle you get more uniform as the number of twist per inch increases.
The mechanism that makes chokes work is lc low pass filtering. If there is not capacitors pulling the cables to ground on both ends… The effectiveness of the choke is lost.
On shielded cables: the shield is most effective when it is grounded at both ends ( then it can shunt both current and voltage)… But really this is going to be a big project…
Instead what you should do is figure out how close your radio can work to the printer… And find a mounting point there
@Camerin_hahn I’m currently planning a complete rebuild of the physical structure, so I think I’ll add the twisting of cables and building an rf shield for the board into that plan.
Agreed that repositioning / procurring a better receiver are cheaper/faster alternatives (it is worth noting that the commercial receiver that came with the transmitter - a B&D Power Monitor - doesn’t seem to suffer the dropped packets that the cheap receiver I grabbed from Sparkfun does).
@Alex_Wiebe my guess is that the receiver is garbage, engineered to a point where it works, then shipped. Places that build quality radios will test interference as part of quality assurance, but places other only test the legally required amount for sale.
I typically use Bluetooth. To get a Bluetooth stamp you actually have to make sure it works with interference. It is part of getting a bluetooth certification. ZigBee, WiFi, and other protocols don’t mandate receiver testing.
If you want to talk emc, let me know. I have been working in that field on and off.
At the risk of going way off topic: This is the page that tracks my power usage. A 2nd green line has been added to the 7 day chart - you can now see when I run my printer by the gaps in data 
@Camerin_hahn Yeah, the current receiver (https://www.sparkfun.com/products/10532) is strongly not recommended for the job - unfortunately it was the receiver documented in the first site I found that claimed some success at logging packets from the transmitter.
I have found a better project to follow, and based on the documentation, I believe the Sparkfun receiver is a super-regenerative board, and what I should look for at a minimum is a superheterdyne board. (https://github.com/scruss/Powermon433#user-content-quick-start)
I believe this one from DX has better noise rejection and is a pin compatible replacement (http://www.dx.com/p/geeetech-superheterodyne-3400-wirelesss-receiver-433mhz-rf-transmitter-kit-green-370793#.Vk32l9KrS70). It’s supposed to be on a boat somewhere in the Pacific right now