How do you break a speed wall?

[furr104]

Seriously. I've been practicing Chopin's etude Op. 10 no. 8 for almost 5 months.
My teacher told me that the only thing that separates me from playing this in public is 5 bars in the middle section. Not the right hand theme, not the coda but these 5 bars for the left hand 

The problem is that even if I practice it with rhythms, after 20 minutes of practice or so I can make it work (till 100/112 quarter notes -- more and my hand starts to crumble), but if I'm playing it in a lesson without prior "warm ups" I'm done, it's a mush, honestly.

I knew my left hand was weaker than my right one but I thought the main difficulty would have been with the runs on the rh, not the left 🤕

There's a baseline speed in which I'm comfortable playing this passage with cold hands, but it's too low (88) -- I would at least need to reach 100.
The problem is mainly on the 4th and 3rd fingers starting the four-notes pattern -- they're uneven after I hit the highest note with the thumb and turn back to the next group

[lostinidlewonder]

Chopin’s fingering forces 4 to stay curved and "unstretching" feeling separated from any stretch after it or returning to it. Moving from the 4th to the extended hand position and back to a "limp" 4th is helpful to promote relaxation. There's so many reason why this passage might trouble you, it is really sad your teacher hasn't given you any solution in 5 months!!!