@Rick Junkin thanks again for helping me figure this all out. He really went above and beyond just to help a rando on the internet figure this out.
The EFIS Editor was nice to use but has a couple pretty big flaws.
1. It's missing validations that will prevent the .ace file from loading on the G3x. The G3x will just tell you "no valid checklist found", and not provide any helpful information beyond that. Opening the file in ACE Editor looked fine as well. Rick took the time to click through each and every checklist page to find errors. Again - cannot say enough thanks here.
2. It will let you / help you use fancy ASCII characters. For instance, it's pretty to have "70°" in the checklist file, but the G3x will not properly display the ° so it's a waste.
Another word of advice. The POH checklists have a lot of extra text and details in them. I copied most over to the .ace to load into the G3x, but when displayed on the split screen there isn't enough real estate to show. I'm going to drastically cut down on the note/caution text in the future.