You're dropping a little too much on the back leg as you begin. Don't overexaggerate this and keep it ramrod straight but don't drop vertically down so much. It seems to be contributing to the head staying back too far. Try a different mental cue here as an experiment. Rather than thinking about firing the front hip, think about a point at the bottom of your glove side lat. Firing that sideways might help stop the leaning back of the head. I toyed with this last night with my son (15 yr. old lefty) and it helped. The other thing was for him to do that very explosively. Really fire it hard. When he did, he had some good "pop" on his fastball.
Also, your glove seems to have dropped since the last video I saw of you. In this video, it looks like it just stays down at the bottom. Get that elbow up and the forearm horizontal during most of the stride. Then either bring the chest to the glove, as Tom House would recommend, or tuck the elbow into your hip and the glove next to your chest. Either cue can work.
And lastly, send me that video!!