Hi Joe-Joe. You say you’re riding dressage tests at a local schooling show at your own facility. Dressage tests are ridden one rider at a time following a pattern of movements so you should be alone in the dressage arena. But whether you ride alone or in a group, it sounds like you need some help from a trainer. You have 55 years experience as a hunter rider so you should have some idea of what is expected of a show horse .
Lower level dressage asks that the horse move in a consistent rhythm, with relaxation but with energy and a desire to go forward a at medium walk, working trot and working canter. No galloping is required. The horse should keep a steady contact with the bridle and show the beginnings of connection via thrust from the hindquarters toward the bit. He should maintain the beginning of straightness, meaning that his hindquarters and forehand should be aligned on straight and curved lines. He should be obedient and confident to the riders aids.
If he runs, there are some serious holes in his training and I suggest you work with a dressage trainer who is willing to ride your horse and evaluate his suitability for dressage and for you as his rider. Warmbloods or warmblood crosses are the breed of choice for dressage and can be found in smaller sizes as well.
Since you’re concerned that time is an issue, get some help and make the most of it. Horses only do what their rider or handler allows them to do. When we can’t solve a problem, we need help from someone who can. Put those 55 years of riding experience to good use and study the mind of the horse. They seem to have human attributes but where they see the world in different ways from us is the key to training them and cultivating their peace of mind and ours. Best of luck for many more years of fulfillment.