Hi,
After writing this, realised that the methods I mentioned here might be too simple for the pieces you are playing

. Better ask someone with more experiece!

al again,
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I'm not a teacher, but rather am a student for life, so I try to pay attention to what works (for me). Perhaps I have some suggestions.
You don't need to play the piece through from beginning to end. That will come eventually-- don't worry about it. What you want to concentrate on are the difficult bits and feel comfortable with them. Since you've already played the pieces through a few of times, you should know where these parts are.
Try isolating them. Just play the difficult bits -- 1 bar, or one phrase, not more. This takes lots of discipline (which I find hard to acquire). But you have to force yourself to stop at the end of the bar, go back and start again.
Bernhard has this 7 times rule. It seems to work for me. Just isolate the bits and play it flawlessly 7 times. Take it as a challenge of some sort. Make sure the fingering is consistent and the sound is clean. If you can put in the dynamics and the required emotion. Sometimes i find that associating a phrase with a texture or an image like a tree in the breeze or, water running helps not only with memory but also with the sound. Also, it is to a challenge to keep your body relaxed and concentrate. Make sure all the notes you are playing and everything you do is deliberate. Already there is a lot to think about.
Once you have done this with a difficult bit, try linking it up. If you are up to it, link the phrase up onto the new phase whilst doing the 7 times rule, so that you don't have this difficulty later. Don't forget to get in habit of breathing in between phases. (Not just musically but physically -- i find that this helps.)
Ok, so say there are 5 problematic spots. Do each of the 5 spots separately. Until you feel completely comfortable and easy to link up. If you still can't manage some of these, reduce the problematic area even more -- into it's component chords, or finger groups, and practice these groups.
Once you've dealt with all the spots. Play the piece through slowly several times (this is to help your brain get used to the length of the whole piece) make sure you relax and concentrate on economy of motion -- this is so that you know the most comfortable and easy way to play the piece. Hopefully, you will remember what to do when you encounter those difficulties again. I strive to get exactly the same feeling after i speed up.
Finally once you're feeling confident, try it up to speed. I don't do it by cranking up the speed slowly. If you've done the 7 times rule properly at the correct speed, you should already have the technique to play at speed. So jump in the deep end! Don't worry about messing up, just work throught the mistakes. Once you're body and mind is used puttig the motions together, you'll find that you won't make many mistakes.
Lastly, don't worry if you have to repeat the process over several days. Somehow, I (as well as many others) find that the way the memory works, is that it absorbs things into the mid-term and long-term memory more slowly than the short-term. The first day that you've got it correct, all the new technique you've "mastered" for the piece only went into your short-term memory. You will find it more and more easy to get through the difficult bits, and eventually they will just stick in your mid-term memory and you find you can just play the piece flawlessly and even have it memorized.
This method of working requires a lot of discipline. At first, i did not quite believe that it works and thought that reducing pieces to exercises was boring and unmusical. There is always a tendency to want to just play everything through, but after experimenting a little, i really find it much better. It works for me. Try it out!
al.