Like MarkKO said, you have to learn to keep a rigid torso. I would recommend to stop deadlifting from the floor for a few months because there are too many things you have to think about to get the lift right and it would take much longer if you continue to pull with the current weights you're using now.
If I had to teach myself how to deadlift back when I first started or others now, I would start off with mat pulls with the bar just below the knees. I would recommend wrist straps because the most important thing to learn first is creating a rigid torso. During the start of each pull, once the straps are in place with the arms straight down below your shoulders, begin to pull the bar a bit to create a little tension. Most of the weight should be on your heels and you'll feel tension in your hamstrings. While pulling the bar, you need to brace your abs, squeeze your lats as hard as possible and raise your chest until your shoulders are directly above the bar (but do not hyper-extend your back). Keep a neutral neck position. Raising your chest up will help you pull slack out of the bar while keeping everything else tight. Once you feel tension in your entire body, you're ready to pull. Follow a linear progression and do not worry about the weight on the bar. If your shoulders go forward then the reps don't count. This training cycle is entirely devoted to bringing up your torso strength and creating muscle memory. Again, do not worry about the weight on the bar or what you have done in the past. Record every rep in every training session and make sure to be strict with form or you will have to keep coming back to fix the problem.
Start off light and add weight each week. More volume is preferred over higher intensity since it'll provide a better stimulus for building strength at this point. When you stall, lower the mat pull height and reset the weight. Ignore the amount of weight you did at the higher mat pull height because it doesn't matter. Pretend that the lower height is a new lift and all you're focused on is keeping your torso tight and keeping your shoulders over the bar. Your quads and mid/upper back will soon catch up to your hamstrings and lower back. Once you get to pulling from the floor, lose the straps when you can continue to keep a rigid torso without grip strength interfering with your focus.
Your hip and knee position should fall into place if you pull with a rigid torso and shoulders over the bar. There could still be other small imbalances but they'll be much easier to fix. You'll have to put your ego aside for awhile because your hamstrings and lower back will be capable of doing a lot more than what the weaker muscles can do.