Yeah first & foremost, rule out/treat any pain/discomfort. Esp if it's been a sudden change, esp if he is OK at a walk but now very unhappy to go any faster, it is a big likelihood that pain is involved. Could be tooth, back or hoof related(or anything else) or could be saddle fit/state, too tight a girth, could be what the rider is doing/ how they're riding(so vetting is not going to rule out/treat everything there).
How long have you had the horse? How old? What's his education 'standard'? What's yours, in regard to horses? Has he generally been good before a sudden change, or have you always argued with him about thing but it's recently got noticably worse?
Assuming it's nothing physical, he's obviously telling you he's very unhappy about something. Perhaps it's fear of something or other on the trail, perhaps lack of trust in you. Perhaps he's leaving mates behind. Perhaps he's a 'bossy' type himself & telling you 'not without a fight'. Perhaps he doesn't understand what you want, so getting towey... Without a fair bit more info, can only guess at a multitude of things.
Whatever the reasion, fighting with him on it will likely only make matters worse. Even if you 'win' it will be at his loss, and he will have a very bad taste in his mouth about being ridden/ridden out. While punishment may sometimes be neessary IMO, setting him up to 'profit' from 'right' behaviours, setting him up for easy success, win/win situations are a far better place to start, in which he will be in a receptive & keen state