Whether it’s golf or something else in life, old habits die hard. In golf these changes are difficult to make because there is a gap in our awareness, a blind spot. Doing numerous quality reps of the right drills to ingrain the new motor pattern in our neurological system is important, but that alone is not enough. When you setup over the golf ball those old motor patterns are going to reappear. However, if you are unaware of them, then nothing will ever change.
When you get to the point where there is a huge gap between the rehearsal swing and the actual swing hitting the ball then working on better kinesthetic awareness is key. A great way to do this is to make slow motion swings which automatically increase your body awareness. Slowly progressing to faster swings and paying attention to specific tendencies will allow for a tremendous improvement in awareness of those tendencies. Of course you can always get feedback from a coach or video to see if what you are feeling is what is actually happening. The key is to make feeling the flaw the main focus. Once you can feel the flaw then you are on your way to closing the gap.
It is not necessary to focus on more than one specific change at a time, but it is important to actually make the change if there is to be any progress. Make your focus more specific, your goal clearer each practice session, and don’t forget to be uncomfortable!