Something I finally pushed through was my mental roadblock. My ankle was thrashed in a car wreck when I was 12. Knee too. I kept telling myself THAT's why I couldn't run at 350, let alone 421. I'm 333 and run. It's not that your ankle won't or that "I need to weight this much to be able to run." It's about getting your body to that point. If weight were the issue I wouldn't be able to run. You're at 320, I'm at 333. I've been working towards running since 421. You'll get there.
Don't know why, but you sir made me LOL there. +rep I must be tired.