I was really interested to hear in the chord stockpile session that @Griff thinks in numbers and not chord names when he's playing. He's not the first pro that I've heard say this. I've tried several times in the past to read and write charts using the numbering system, but always end up back with chord letters because I realize I'm not thinking in numbers. I end up seeing the number, equating the root, and then pulling the chord name from that. "I need a IV chord, and I'm in D, so that would be a G" rather than just thinking IV and playing a G. That requires mental gymnastics and just isn't efficient. I think my biggest problem is that I get frustrated and fall back on chord letters too quickly. How about a mini-course that focuses on reading and writing charts using the number system? Kind of like a language course in school. In the first chapter use some chord names along with the numbers just to get used to seeing them, and then the rest of the course use only numbers. A chapter for reading numbers with 2 or 3 songs of reading numbers, and then a chapter on writing charts with 2 or 3 songs where we need to write the numbers. I know that this is something I could probably do easily enough on my own, but I have trouble staying focused on it. I'm imagining if it was something in course form, it'd be a little more easy to stick with it.