I’m gonna be rude lol.
There’s absolutely no shortcut.
Practice at slow tempo with a metronome and make sure you play conscientiously every note on time.
And then increase slowly the tempo.
Not rude at all. I have heard this said over and over, and I've also heard it said that you have to just "go for it", that you don't get fast by playing slow.
I do both, with 1 exception that I'm going to change:
In the context of 16th notes, I have this weird zone from about 90 to 110 bpm where I have trouble staying in sync. My understanding is that's where we have a transition in how we play, not unlike when we switch from walking to running. And it happens at different tempos for different people.
I think of it this way: It would get really awkward if we simply continued to walk faster, at the point where we need to start running. And according to a few lessons from what I consider to be guys who know what they're talking about, you switch to using different muscles past that transition zone.
So I've been bypassing this zone, partly because the solos I'm working on aren't at that tempo, but mostly because if I jump up to around 120-145-ish, I can play it fine. I can manage up to about 160, depending on what it is, but it starts getting sloppy.
So last night I spent probably 4 hours working on several picked 16th note solos, starting at 80, and gradually increasing until I finished for the night at 100. I only advanced the tempo when I played whatever it was perfectly, 5 times in a row. And I paid super-close attention to not letting anything get tense. Also did lots of double-speed bursts.
I don't know how, but even though I
can play these riffs clean at faster tempos than that transition zone, I think there IS something to be gained by being able to play whatever it is, at
any tempo up to our current maximum.
So maybe adding this "method" to my practice will help with my OP.