He could just be trying to figure himself out. If you have acess you could put some poles on the ground so he has to pick up his feet. Now I'm not sure how any gait other than walk, trot, canter and gallop work so I'm not sure if it would help.
Are his feet too long? I knew a horse that as soon as his feet got a little too long, he would trip alot. Also, Navicular can cause a horse to trip a lot but the chances of him having it at this age is pretty slim and he would have shown other signs of soreness before.
I hope this helps
"You know, for as long as I can remember, I've had memories." ~Colin Mochrie