I have had the same issue with my AQHA gelding. It would take hours to get him the trailer. But he would end up getting his nose cut or something like that. He wasn’t scared, just stubborn. We took him out and did some serious groundwork with him. Also more desensitizing. Then we took him out and would try to load him. If he wouldn’t load right away, I would have a helper VERY GENTLY swing a whip back and forth near his hocks. We have, in the past, tapped his hocks as well.