I'm not sure how long you've been doing pullups, but you have some faulty movement patterns ingrained and no matter how much weak point training you do, you'll always revert to that faulty movement patter.
I'll give you two methods in fixing these faulty movement patterns.
Method 1 Greasing the Groove:
This works great if you have a pullup bar at home or near you. Essentially what you want to do is lift as a submaximal level but with perfect form. So for example, if you can do a total of 5 pullups in a row, do 1 pullup. You read that right 1 perfect pullup. And do that every hour. Once one pullup becomes too easy, do 2 pullups every hour. And keep building from there. This may seem like it's extremely low volume, but over time it builds up QUICK. Say for example for 8 hours out of the day you do 1 perfect pullup. That's 8 pullups a day and by the end of the week that's 56 total pullups. PERFECT pullups might i add. And as you get stronger the total weekly workload will increase.
So why the submaximal reps? Well it allows you to ingrain perfect movement patterns and you stop before fatigue settles. This is the quickest way to ingrain proper technique.
Method 2 Dynamic Effort Pullups:
Similar to the previous method, dynamic effort does the same thing but within a workout. So for example, say you can do 5 clean pullups. Great! Now do something like 10 x 1. That's 10 sets of 1 rep. Rest 30-60 seconds and do another set. The point here is to practice a perfect pullup every rep without fatigue becoming a factor. Once 10 x 1 is easy; Not when you can do 10 x 1, but when 10 x 1 is really easy, the reps are fast and the form is good, progress to 10 x 2, then 10 x 3; hell even 20 x 1. Essentially higher sets lower reps.
Technique When doing pullups, your first contact are your hands. So when you do each rep, make sure you squeeze the bar. This will engage your forearms more and you'll be blown away how much more stable you feel with just this simple tip. Next, when you pull, imagine pulling using only your two ring fingers (this is the finger between the middle and pinky). Idk why, but I've found that people can engage the proper muscles more with this cue. Finally, I really think you should checkout Brian Alsruhe's channel on pullups. He has a pullup technique guide that is stupid simple.
To summarize, you practice perfect technique and stop before fatigue hits. Keep doing this for months and watch as your form, strength and size explode with each week you do this.