I had just about had it with my 4 year old TWH gelding, Pegasus. I posted him for sale on 4 different sites and was trying to detach myself from my love for this horse, in case anyone wanted to buy him. I had talked to several people over the past year about how "wired" he had become and how unmanagable he was getting. I was visiting with a trainer in Leipers Fork and she asked me if I was giving Pegasus any sweet feed. I had been giving him half sweet feed, half oats almost every day since I bought him 2 years ago, as I wanted him to gain a little weight and muscle up some. She suggested that the sweet feed was like "giving a chocolate bar to a hyper active kid, then expecting him to sit still." I immediately cut out all the sweet feed and cut back on oats to a couple of cups after a hard ride. A week later he was about 50% improved, 3 weeks later he was a totally different horse. He no longer spooked at everything on the trail, was calm and was much easier to get into gait! He is actually a pleasure to ride now, stays collected and in gait.
I don't know why I decided to give him the sweet feed in the first place, but I would advise you to eliminate it if you are having any control problems with your horse. It is a very simple solution to a very serious problem. Pegasus's entire disposition has improved and I am removing him from the "For Sale" sites on the internet.
Good luck and good riding!