I've just come across this thread and it resonated with me quite a lot.
Since I have a digital piano with a midi output I have been running through the exercises in Piano Marvel (www.pianomarvel.com) slowly trying to play all of them and score 100%. There is a "Method" section and a "Technique" section. Each section has six levels (1 to 6), each one harder that the last. Each level is broken down into 5 sub-levels (A to E) and each sublevel has approximately 20 exercises. Amongst several options is an "Assess" button which when you click it starts a process where you get counted in and then have to play the piece at the correct tempo. You get scored as to the proportion on notes that are the correct pitch and at the correct time. It also colours the correct notes in green, incorrect (in time or pitch) in red, and uncoloured means you never played the note at all.
Up to the middle of level 3 I was just playing the pieces. It might take a couple of goes to get it exactly right, but it didn't take long to iron them out. But at the middle of level 3 the difficult increased and the rhythms and note sequences were not straight forward. I then had to use practice mode, where the piece is broken up into a few bars at a time (and sometimes you can also do RH and LH separately before bringing them together). These start at a slow tempo, then move to a faster tempo, and finally get you to practice at speed. The Assessment is exactly the same as playing for real.
So I found the trick was to run through the practice sessions in detail, starting at the slowest tempo, stay there until I got 100% and then repeat at the next highest tempo. Eventually a practice session would start combining these few bars into longer sections until eventually the whole piece had been practiced and conquered (ie 100% scored). I eventually have succeeded with every piece up to the end of level 4, where things have got more difficult.
When I was (a lot) younger, I read the "Inner Game of Tennis" (got to it from the "Inner Game of Golf" as I was a golf beginner at the time). That talks about the two selfs. The number one self is an Sergeant Major sort who tried to order you to do things, and the number two self is a quiet but very capable individual, who if you just trust in him would do the job. The big trick is to get the Sergeant Major to get out of the way so your number two self can function. In fact, if we can set up Number One to provide additional awareness as to was is happening, then even better. One exercise the book talks about is called "Bounce Hit". You get your Sergeant Major self to call out "Bounce" at the exact moment the tennis ball bounces on the court and "Hit" at the exact you hit the ball with your racquet.
I have a couple of very tricky exercises at level 5 where my previous strategy had not produced results. The hardest exercise so far is where I had to try o play the Hannon #5 exercise at speed. It actually split this into 3 exercises, RH separate, LH separate, and then Hands Together. I scored 100% in the Hands Separate at full speed fairly rapidly, and even Hands Together at the slow and medium tempo. But try as hard as I could I could not get above about 95% at full speed. The problem was always with the descending part of the left hand. The fingering is 5, 4, 5, 3, 4, 2, 3, 1, slowly moving down an octave on note at a time and I was finding that I had not played the second 5.
I did the best I could to get the Sergeant Major self to explore was was happening to my left hand without trying to control it. I eventually (at about 90 attempts at the exercise in) could see that climbing up the scale my hands were going in a sort of gentle rotate/rock motion , but coming down the LH pinkie wasn't coming off the key after the first hit, so couldn't play the second go as the key was actually still slightly depressed from the first attempt. In the end at about attempt 120, I found a quite deliberate attempt to roll my arm quite violently to play the notes solved the problem and I eventually did score the 100%.
I had another problem in the Method Section of 5B where a piece called "De Colores" had almost the entire right hand playing thirds at speed. I had tried returning to the practice sections, but the bit that I kept getting wrong was right on the join between two of the practice sections. This time I solved the issue by practicing independently of Piano Marvel, and then whilst doing the actual Assessment using the Sergeant Major as observer technique to watch what I was doing. Somehow time appeared to slow down and as I approached the place where I was going wrong I suddenly had time to know what I should do and watch me do the right thing. Really weird.
I've been using Piano Marvel for just short of 3 months now, but its only been in the last month that the level I am trying to succeed in has been tough. But in this last month I must have worked through about a fifty exercises where the learning was more complicated than just a straight forward play the piece a few times to learn it and get a 100% score. But the process of breaking it down, taking a little bit slowly, initially scoring poorly on that section, but then watch it come together at 100%, then put the sections together and again watch the score again soon get to 100% that I am now confident in this as a way to solve the problems.