I think your technique is coming along nicely. How much practice are you getting? I think you just need to log in some hours.
Here is a link to my thumb movement thread. I need to up,lad a new clip as I’ve studied a bunch of players and revise my thumb motions. Basically emulating Miller but much more exaggerated. Now anytime I’m changing strings on an upstroke, I extend my thumb backwards, and vice versa for down strokes. Kind of like my thumb is the end of a whip. It’s helping a lot with tracking and percussive power when desired also. Anyway I didn’t get a chance today but I’ll try to get a new clip up tomorrow