Well, today after cleaning up the mess Gus made the night before, we went for a walk outside today. He was really forward, which was nice. He moved right out of most of the stiffness. I think we walked around a mile today, maybe 3/4 of a mile, but it was a nice distance. Walked to the top of the hill and back.
Gus was tracking up very well with both hind legs. No real bad steps. Forward and energetic. Happy. It was nice seeing him so enthusiastic. I'm going to contact the vet again and see what our next step will be.
Back in May/June, Dr. T (the specialist) recommended daily walkings. Then we progressed to 5 minute walks under saddle, progressing up to 30-45 minutes over the course of a few weeks (like three). After he was worked (at a walk) under saddle, he got turned out. That regime worked really well and he was returning to soundness, slowly but steadily.
The only problem with that plan this time though is that the turnout is causing more bad then good. He's turned out with another horse and I think that is about 90% of the problem. So, I'm looking forward to what Dr. N recommends. I'll keep this updated.