Controlling pace of Backswing

I'm hoping a little advice here will go a long way. I am swinging just a little beyond half-swing and have tried developing the left hip on the start of downswing. Trying also to sense the right shoulder tilting.

https://saguto.golf/courses/865895/lectures/15769568 Practicing without cub is fine but with club in hand, I find my left knee is feeling too loaded, often kicked towards the target - basically attempts to shift hips results in them shifting off line and anyone standing to my right risks assassination.

I moved on to the subsequent section and this has I think provided the reasons for many of the issues - tension. https://saguto.golf/courses/865895/lectures/15739994

I know I can manage a steady paced backswing and then an easy gentle shift on the downswing with a wedge or a 9 iron. An 8 iron - 6 or 7 out of 10 balls. When i try a seven which is the limit of my practicing at the moment, I know the start of the swing is fine but then the club accelerates back like a runaway train and chaos ensues.

I'm sure others have experienced this and would love any advice that helps control the pace of the backswing.

It certainly a testament to the quality of Tom's teaching methods that I have learned so much in such a short time, and am developing a sense of where I'm going wrong. Man, this is such fun.

Thanks.