There are some very nice things happening here. At full video speed, it kind of looks like there's very little whip happening in the throwing arm and looking like you kind of push the ball. I was lucky enough to hit the pause button at just the right time and it does look fine.
jd might have the right idea here in that a less than game effort could be the issue. More sideways momentum generation, over a longer period of time, may solve the stride and trunk flexion issues.
All in all, nice work.
ps. Why the little glove waiving bit before you start?