I can't thank everyone enough for all the feedback in the comments section of my last post. In particular, breeding/pedigree/lineage is not my forte. It is so helpful to have those of you who are, weigh in.
I'll try to describe how Tex is reactive, since I don't think I was clear on that point and the question was asked: how can Tex be so solid and calm in what you teach him, but still be reactive?
The reactive part of Tex is almost like a reflex. It feels disconnected from him. I'll give some examples:
When I go into the boys' pasture, Tex always looks up and walks over to me in a relaxed and friendly way. Then he stops a few feet away from where I am standing (I always wait for him to come to me). I say "Hey Mr. Tex Mex, how are you doing today? " as I extend my hand, palm up in greeting. He stretches out his nose and touches my hand, then I move to his left side and touch his neck, above his shoulder, firmly but gently; I don't tickle him but I don't pat him either. Invariably, he flinches at the first touch. "You goof; it's just me" I say. I rub his withers, the way horses do when they are grooming each other, and he immediately relaxes. But he always, always flinches first.
At the clinic, as I lunged Tex yesterday he was relaxed and tuned into me. If I walked fast, he would trot. If I slowed, he would walk (eventually). To get a prompter transition, I worked on moving him onto a smaller circle while walking slowly until he came to a walk. Then I praised him and we did it again. We did the same thing with transitioning from walk to halt. If I stopped walking, he was supposed to stop. Initially, he just kept on walking - slowly and in a relaxed way, but still walking. I reeled in the lunge line until he stopped. He caught on pretty quickly (he is a smart horse), and after the second time when he nailed it, Mark said "go up to him and give him a rub; praise him." So I did. And he flinched when I touched him -- even though he was standing quietly, watching me. He wasn't alarmed, but he reacted like it was the first time I had touched him.
Mark watched this happening, over and over, during the course of the three days. He didn't say much until the end; I'm sure he was waiting to see if Tex would work out of it and stop reacting. On the last day, Mark walked over to Tex (calmly, in a non-threatening way) and Tex ran backwards. I laughed "stranger danger!" -- and Mark shot me a look. He said, quietly (because he is a quiet guy), "I'm not a stranger to this horse."
At this point, Tex runs from everyone except me -- and sometimes not from Brett. But even with us, he still flinches or steps away or reacts.
Mark did say that often horses, especially ones who are as easy to train as Tex, are often pushed too hard in their early training.
I think Tex has a couple of strikes against him. Time will tell whether they can be overcome. I'm not giving up on him, by any means. He has a lot of lines going back to Driftwood -- being inbred is a problem to start with and Driftwood was a reactive horse. Thank you to all who pointed that out (I didn't know anything about Driftwood other than that he was a successful competition horse and sire). So, he's got a double whammy of reactive in his genes. I'm quite certain he was treated roughly and it is very likely that he was overloaded in his early training. The amazing thing to me is that he has remained sweet and kind, and that he tries hard to do what is asked. There isn't a mean or aggressive bone in his body. Just fear and reaction.
Mark said that I am doing everything exactly right with Tex. I'm giving him clear instructions in a way that doesn't cause pressure. He feels safe with me. The reaction is greatly reduced from when I started working with him, but it still exists. Until it is gone, it isn't safe to ride him. If he reacts to something, he will flee and ask questions later. And apologize. But, I can't afford to be part of the reaction from his back. He's tall and strong -- the chances of me getting hurt in the reaction process are too great.
I am going to continue working with Tex. He is improving and he is becoming affectionate with me. I'm going to research doing fancy ground work with him -- kind of like dogs on an agility course -- teaching him to weave through cones and such. I think it will be fun and it will help me to have a goal in my work with him. If he stops reacting, I'll ride him. If he doesn't, I won't. Mark said it would take at least six months for the reaction to go away and most likely take years. That's fine. I have time -- and I have the lovely Lucy to ride.
I'm also pursuing a full medical work up -- and I will include Lyme disease in the blood work. My vet is very thorough and I am going to ask her to explore all possibilities. We have an appointment next week.