Well, let me start out by saying I used to throw EXACTLY the same as you do (albeit, a higher leg kick).
-From what I've learned, you need to slow down a bit. Of course, not your arm, but your wind-up. Lift your leg and make sure you're set in balance, then push off and let momentum and gravity pull you down onto what would be the mound. Also, when you're moving that fast, your arm has to move twice as fast b/c it goes behind your back and all the way around. Don't swing your arm so far back because it has to eventually catch up to your fast-moving body. Then, as you plant your foot, violently snap your glove elbow down to your side (glove in chest) and allow that fast arm you have to start closer to home plate. You throw hard, but you'll seem faster if you get that power w/ your body and not behind it.
I hope that makes sense. But wow, that is exactly how I used to throw, and since changing the stuff I mentioned above, I've never had a sore arm after pitching. Plus, the ball is released farther than it was before and with more power. Good luck,