Part of what is slowing you down in the middle is that you are straightening the legs too much too soon. Because your legs are extended too early, there is a bit of a pause for you to correct the position at that point. By the time the bar is at the knee you want the shoulders right over the bar and the knees still slightly bent.
I would suggest trying some segment pulls, followed by regular pulls or cleans. The goal should be to hit good positions on the way up and then hit those same positions without stopping.