On NOT speeding up, immediately after you can play it slowly... Maria Luisa in progress

I have to admit it.  I'm not a patient person.  Despite my best intentions, I'm always speeding up a piece before I can really play it.  Not to mention running the whole thing instead of just practicing the difficult bits.  I know this is not the way to do it, and indeed for the last few pieces I've made a definite attempt to get more focused, stop, and slowly concentrate on the bits that are eluding me.  I'm still only partially successful though. I practice it slowly until I get it, then speed it up and sometimes it works at tempo, sometimes it doesn't.  Last week my guitar teacher pointed out a part I had practiced slowly but it was still hit or miss on the play-through. He gave me the instruction to practice it slowly and NOT to speed it up for the whole week.  Well, a whole week is a long time (!) but I did manage not to speed it up for several days, and lo and behold, I can now play it quite reliably.    So this was something of a revelation - (Duh, you might say).  I actually needed to continue to play it slowly for many more repetitions before speeding it up.   Hmmmm.  So maybe that's why my slow practice isn't working so well.  So to test this theory I'm going to go back to some of the problem parts in Maria Luisa by Sagreras (as evidenced in the video - there are quite a few of those!) and run them slowly until they are thoroughly ingrained... and when I can finally play the notes reliably I will be able to start adding the dynamic variations - I know,  experts say they should be there at the beginning, but I'm still at a stage where one thing at a time works best.