It could take months or even longer for him to get rid of that attitude. He would need guidance for it, too. If you don't want to get rid of him I suggest working with a trainer so you can understand what to do and the horse can get guided by someone with more experience.
A horse that is gelded late may never realize they are actually gelded and may for quit sometime think they are still a stud and have stud tendencies. Unless you want to invest yourself into researching the heck out of how to deal with this situation and live with the fact that the horse is going to do stupid things because he doesn't know any better then I suggest either a trainer or another horse. Something that has a hundred thousand miles on it.
Someone out there has got to be wanting to trade in their slow poke horse for something a little quicker.