I also agree that fixing your position is the best place to start after ruling out pain evasion. I can't tell you how much better my own horse travels when I really take responsibility for how I travel. It's a work in progress, and old habits die hard, but it's really worth it.
I recommend picking up a copy of Centered Riding by Sally Swift. I just ordered it myself, and can't believe I waited so long to get it. Excellent book.
Thanks for posting that link, Bandera! :)