You could always try the old trick of breaking a continuous, fast passage into convenient small sections, each of which you can easily play at speed, separated by small pauses. Then gradually eliminate the gaps over time. This has worked like magic for me in the past, although I haven't the slightest idea why it should have.
This works well for me too. Besides, it makes your practice more efficient as you get the time to practice the difficult areas more times ... (Slow practice takes a lot of time, in case anybody hasn't noticed ...) Normally there are just a few areas in the piece that are this difficult - if there are many, or if the whole piece is that hard, then I would say you should move on to something easier.
There are some other little learning tricks as well: if you see an arpeggio forming a chord, then play it as a chord first, until you are dead sure how to position your fingers.
You can bounce on every note, for example 4 times in a very fast tempo, then 3, then 2, then 2+1 and 1+2, which will work up fast movements even though you get some time to think ...
You can also play a "skeleton" - simplify the piece to a rough structure, for example play just every 4th note in long runs - but be careful not to change the original fingering because otherwise you'll be in trouble later ...
Personally I also find it useful to practice fast passages in a dotted rythm, which is another way to say "one note fast, the other slow". Just be careful to change that rythm regularly before it gets stuck with you; it is a tool for learning, not a habit to form. I usually change the rythm after 3 repetitions.
If it is written staccato, practice in legato or divided legatos, or the opposite.
A very difficult exercise is to play some - plan in beforehand! - notes in ff and the other in pp, and to do a different pattern with your other hand.
Will these exercises sound good, sound like music? No, probably not! But the whole point is that you teach your brain many, many different ways to play these segments, and you are also forced to stay concentrated every time you play them. When you play exactly the same segments/pieces exactly the same way, perhaps just with a slight gradual increase of tempo, you will form a lot of bad habits on your way, including little muscle tensions and jerks that you will enforce in every repetition, until you just cannot get rid of them again. And there is your "speed wall".
If you constantly change your "parameters" you will avoid those built-in tensions, and you avoid the autopilot trap, and soon you will find that you can play just as you decide to play - including fast, even and correct. Besides it is fun.
The secret of playing real fast is to be as relaxed as possible, which you will be when you feel that you have total control of your playing, every keystroke.