Just a thought--is it possible that in the effort to decrease spl, you are creating tension in your body that shouldn't be there? While I can't identify with your balance problem, I do remember when I first started TI, it seemed to me that spl was what to concentrate on. I got so uptight that I used whatever energy I had to decrease spl. This caused me to run out of air and my rest periods were longer than my swim times. Now the mantra seem s to be optimal stroke, optimal spl, etc. etc. Suddenly the lower spl doesn't seem to be important. Now the talk is all about gears and different spl at different rates. so who knows what will be the next all important thought process?
But since you are improving, maybe you are on the right track. I admire your determination and wish you well.