Yeah, I’m a moron, the issue was frame rate. I work almost exclusively in 23.98 but this client prefers 29.97, that solved the problem (mostly, there’s still a tiny bit of jitter here and there, but that is corrected in compression, so I think it’s just an issue in quicktime?)
My computer is definitely up to the task, 2013 mac pro, I was just too set in my 24p ways. Still haven’t seen a solution to the rolling credits issue though, that I KNOW was the right frame rate in all respects.