I agree with all here that your mechanics look very good for the most part.
What Roger saw as a leaning motion, I saw somewhat differently: Judging by the stationary objects in the background of your video, it looked to me like you start out ‘tall’ and drop down to a lower posture early in your stride. With better video (use a tripod!) it would be more clear, but that’s what it looked like to me.
If you agree that you are doing that, you might want to start in a posture that has a little more bend in your knees so there is no wasted north-south motion in your stride to home plate. Obviously, since you are throwing down a slope your head/shoulders/torso will track down the slope of the mound; but your head should stay parallel to the slope, not drop down (or pop up).
Other than that one thing, I think you have a real good delivery.