Wow, I think your getting a bit of a harsh time on this thread!!!
Kudos to you for going back to the ground, and checking out every possible issue.
I had a horse similar, but not the same. He was amazingly strong, and had a great stop, but not a very good slow down. His main problem was slowing his canter, to the point it was walking speed, before dropping back to a trot. In his case, I found the more leg I used on him, and the more I pushed him with my seat, the more he rocked back on his haunches and actually steadied and relaxed.
I tried many different bits (all snaffles) on him, until I found one he liked. I had my success with a Myler bit. It was a Myler low port comfort snaffle. he reacted well to having the extra tongue relief. It was this bit, without the hooks (holes to attatch the reins for leverage)
(sorry about the size!)
The myler bits are expensive, and a lot of horses don't need them, but if it works for your horse they are worth it.
Let me know if you want anymore information, etc.
By the way, I haven't had a trainer in about 8 years, and i'm doing fine :] I understand not being able to have a trainer, wether it be cost, location, etc.