Welp - I think we can close this thread.
I hooked up a Dell10v (yeah yeah, me and my commodity hardware…) and it runs just fine. No stuttering, no stumbling.
The original raspberry pi I was using was a Model B, version 1 (https://en.wikipedia.org/wiki/Raspberry_Pi). I even overclocked it up to 900mhz and still saw the stuttering. The issue was the planner buffer was getting saturated (I could see it get full in the grbl widget). As I understand it, that means that the Shapeoko Grbl board is waiting for instructions. I understand it’s just waiting a few milliseconds, but it’s stuttering none the less.
The Raspberry Pi 3’s have a 64 bit quad core 1.2 Ghz processor. That’s 2x the power of this old Dell 10v (roughly).
Again, the goal is to create a dust proof CNC setup so I’m off to find one of those bad boys.
Hope this helps someone out!