My horse i just got is acting hot too. What i've been doing is my desenceitizing him. Taking a long leadrope, with tassles or something on the end to make it a little bit heavyer. stand on one of your horses sides, at a 45 degree angle, and swing the rope over his back. He may jump, and spook a little, but you have to try to go with it, dont pull against him, go with it, and wait for him to talk down, then do it again, slowly work your way up to a longer line. Then do the same thing to the other side. Next you need to senceatize him. So then you lunge him, but to get him responsive, and using the thinking side of his brain, you need to do this: You will need a long whip. Start off by lunging the horse in one direction, then if the horse is going to fast, or you simply want him to stop, pull the longeline inwards towards your bellybutton. and with the other hand step out in the derection of his hindquarters. He should stop, but if he dosn't, try again. This is getting him to think, and that is the first step in getting your horse to calm down. And be respectful. work with going both directions. When you are completed that, do some descensatizing again. (oh and when you are lunging, wait for your horse to lick its lips, or blink his eyes, that shows hes using the thinknig side of his brain).
Work on that for a while, and then when you are eventually ready to go under saddle try this. If your horse does not walk, trot, or go whatever gair you ask do this; if you are trying to get your horse to simply walk, and he is trying to jog, or go faster then that, turn him in a circle, bending him ( if he was a barrel horse, he should be famillular with bending) go both ways, and keep going untill he stops, then try again for a walk, he probably will keep try to jog for a while, but you need to keep circling him. Same with any of the other gates.
Hope this helped