I've been told that with a four step approach, the ball should start into the swing with the first step.  In the video, it looks like you have completed your first step in your approach before moving the ball into the swing.  I think your timing is late.  This causes you to rush the swing, possibly muscling/pulling the ball in order to catch up at the foul line.  Makes it tough to be accurate and keep balance at the line.

I think starting your swing earlier in coordination with your first step will improve/solve some of the other thinks happening toward the end.

See this as an excellent example:

4- and 5-step Approach by Chris Barnes: http://youtu.be/OoyRbBHXQOA

Scott

I think that the arm swing may be what needs to be worked on. Your body finishes at the line and you arm is still behind you coming through. The force is what seems to have you off balance at the foul line.

Balance at the foul line is something I work on often.

Your last shot looks a lot better at the line.

+1

Strapper Squared is 100% correct, your timing is considerably late and the video he linked really is one of the best instructional videos showing the basics.

One other thing that stands out to me is your left arm, it's out to the side through your whole approach.  It appears to me that the the still left arm acts like a spring, taking the momentum of your ball coming through sling-shotting you off balance and also causing you to miss left.  Try to get your left arm out in front of you like Barnes does in that 4/5 step video and don't worry about forcing the arm back, it should come back naturally.

As another bigger guy, I had the same issues with the getting my hips around the ball, without creating a problem with my armswing. What I have been told to do by my coach is this: Line up as your normally would for your strike ball. Once set, turn your feet about 45 degrees to the right. Then take your first step straight toward the foul line as you normally would. With your feet turned, in order to step straight, you have to swing your hips left, which then creates a path for your armswing. It has seemed to work for me.
 
I also tend to muscle my armswing, and am working on that. A good way to practice not doing that, based on a lesson with Mike Jasnau is the no-step approach. Take your ball and step up to the foul line. Set-up in your finishing positions (knees bent, right leg behind and out the left, etc.). Once there, swing the ball and release it. If you fall out of position, you have tried to muscle the ball. You should be able to maintain the position, and the ball should get down the lane. If it goes straight left, it is also an indication you have muscled the swing.
 
Good luck to you.

Starting the ball sooner and reaching with the left arm ain't gonna get his ass out of the way for his swing to be able to tuck in.

If you want to improve find someone to take a lesson from.  It is not a simple fix that starting your push away a half a step sooner is going to magically cure everything.