I think I remember you posting a video of him a few months ago. I remember you saying the part about him being trained in Rolkur. If this is the same horse, he's definitely made some progress. Yes he has a way to go, but he's not so fussy with his head as before. To further your progress, I would suggest using your seat a little more to influence his trot. When he does start to brace or speed up his gait, just soften your posting slightly until responds by softening. (don't change your rhythm, just soften so your like powerpuff on his back). Softening your posting takes the fight out of the equation and it keeps you out of his already over-sensitive mouth. He should soften in a few strides and then you can resume asking him to go forward correctly.
The other thing I would practice with him is stretchy circles. Use the above technique while asking for a nice big working trot on a circle. Keep softening him in an attempt to allow the circling affect to create the inside leg to outside rein affect. Once he starts chewing on the bit, ie accepting it, let the reins slip a litte in an attempt to make him stretch forward into the contact. If the 20 meter circle doesn't work, try sprialing in and out.
I recently did my first show with my horse's first show too. He didn't spook at the judges booth, but his end halt took at least 30 seconds since he proceeded to dance and jig around in place before finally coming to a halt. We got a 3 for it! You took look very nice together. It has to be difficult to work with a horse who was trained that way.