He certainly does sound like he's got your number. Is there another rider you can put on his so you can see a different result for yourself? None of us want to admit our horses take advantage of us. When you see it right in front of you, it tends to make you step up a notch.
At least it sounds like it's a fairly recent problem. It should be easy to correct. Like everyone else said, you are the boss. He runs when you say so, and no other time. Really mix it up on him and keep him guessing and looking to you for what's next.
You just have to see your distance...you don't have to like it.