He isn't visibly lame, not dragging his feet, limping, etc. He doesn't have any sore/warm spots, or any injuries that I know of. He does have shoes, and the farrier just replaced them Friday.
At first I thought it was just the rider, when I first noticed was when my friend who never had ridden a horse before rode him and was pretty unbalanced. But I think I have a pretty good seat, and he still trips. It's mainly at the trot, he does trip at the walk but not as much and he is fine while cantering. I ride mostly western and I post while trotting. I ride mainly on level ground too, and there aren't any holes or things on the ground that he could trip on. We normally warm up for 20-30 minutes before a ride, so it isn't like I am hopping on and cantering off right away.
I forgot to ask my farrier about this Friday, but he has to come back in two or three weeks to trim our other guys(new horses screwed up our schedule lol) so I will ask him then. His coggins Expires in two months, so I could ask the vet then.
Could he just be lazy or unaware of where he places his feet? He does clip his front hooves with his backs from time to time.
Any ideas of what, if anything, could be wrong?