Hey Vince, I just looked at your videos. I think there is a fundamental element missing from your serve altogether, not just your kick, that you should address first. For me, the most revealing video is the side view. It shows that you are basically muscling your swing with your arm and not getting much help from upper body involvement. At the peak of your toss, your shoulders are almost level and you have almost no upper body rotation. It looks very similar to a Jimmy Connors' type of serve. So, before you can gain much improvement on your kick, I think it would help for you to address this fundamental issue first.
In my view, the serve is analogous to the modern forehand in that the trophy pose (your posture at the peak of your toss), is similar to the "load up" position (at the back of the backswing), of the forehand. In both cases, you want the position of your entire body, legs, hips, upper body, shoulders, arm and racquet, to be in the optimal position to initiate a chain of events that will help you to gain as much racquet head speed as possible. Racquet head speed can be used to impart spin and/or power as you choose. The type of spin you impart is determined by the direction of the swing path as you make contact with the ball.
Simply put, at the peak of your toss, you should turn your back to the target sufficient that your opponent could see your name if it were written across your shoulders, about a 3/4 turn. Further, as a lefty, your right shoulder should be as high over your left shoulder as reasonably possible. (Picture a golf swing with your spine tilted back instead of forward). One way to achieve a good tilt is to slide your right hip forward in the trophy pose. When you turn your back to the target forward for you will be about at the left net post. From there, rotate your left shoulder up to the ball dragging your arm and racquet behind it so that the shoulders reverse positions. The bottom shoulder is now the top shoulder. That upper body rotation, in that way, is a missing element in your service motion.
From there, hitting a kick serve is just a matter of swinging up and across as you make contact with the ball. One way to achieve that is to maintain your turn a bit longer in your upward swing. But first, I would recommend that you get comfortable with improving your upper body rotation on your serve generally.
Check out Pete Sampras' trophy pose and upper body rotation here: