I started a thread in the Training forum looking for suggestions on working him in a correct and engaged gait. It's listed here: Correct movement - engaging his back
I rode him in a D-ring snaffle (he used to have an egg-butt snaffle, but I'm not sure where it is and he seemed to do fine in this). Good news: 1) no head tossing with the snaffle, and 2) I free-lunged him beforehand, but didn't "pressure" him - just asked for a lope and stood still. Every time he began loping, he'd start on the correct lead, then go to cross-firing at the same spot (which I noticed was where he'd cut a short corner on the roundpen as well). In support of my "overthinking" theory, if I stood still but kept him at a lope by cuing him with a kiss, he started loping on the correct lead consistently. By the time we were done (which wasn't long), he wasn't cross-firing anymore. I think I just need to let him relax and figure himself out - this method worked a lot faster than "getting on him" and making him work harder! Goodness, what an emotional horse!
I did record my riding today and posted a video in the other forum, but I'll also repost it here so it's in context of this conversation. I took the suggestions to heart and have been doing a lot of research on what collection really is and how to achieve it. I thought "long and low" would be a good place to start, since it encourages them to relax and engage their back. Let me know what you think