Using the video and calculating time and distance, I have arm speed at 68, your release at approximately 62 (radar reading) and 55 at the dish. You can do the math yourself.
41.25/(time from release to the plate in seconds) = mph
You need a 0.589 sec reading to have a 70 mph release. The ball is never traveling faster than when it's in your hand and from the millisecond the pitcher releases it, the ball is actually slowing down.