If your horse is not reacting to you immediatly upon you cueing him for a transition, he is either behind your leg or just plain not paying attention to you. When you are riding alone, make sure you are listening to your horse. At any given time, you should be able to change gait in one stride. Assuming your cues are correct, get your horse's attention by really mixing it up. Do a bunch of transitions between gaits, within the gait, throw in circles, serpentines, halt, etc. Every 8 strides, do something different. Above all, make sure you are asking for the transitions with your body, not your hands. Keep your hands in front of the pommel and make sure they stay there. Quiet hands, active riding body. Hope that helps.
You just have to see your distance...you don't have to like it.