I’m going to guess that you aren’t practicing slowly enough. Almost no one does. But professionals do. Strangely enough it’s the most efficient and often fastest way to learn new material.
Generally “slowly” is the only speed at which we can play something unfamiliar. How slow? Slow enough to play it without mistakes. If you’re making mistakes then it’s not slow enough. When should you play it faster? When you can do so without making mistakes.
It’s an incredibly simple formula but it requires that we be painfully honest with ourselves. It doesn’t require judgement or critique, all you need is awareness to notice a mistake. And if you aren’t finding mistakes then you aren’t practicing, so go find some mistakes and slow down.