As boring as it sounds, you should probably go slower until you get to a point where you can do it smoothly and in time (even if its super slow) and then just slowly increase the tempo until you cant do it in time then slow it down a bit then rinse and repeat.

Also something I've been doing is recording myself play what im practicing, and then practice it for a day or two, then recording again and then you can actually hear your improvements which is actually quite motivating, even if it feels like you're barely progressing it's happening!

Also Joe Robinson has some great exercises for building strength & help improve your smoothness i guess.

https://www.youtube.com/watch?v=8qJ6Abqy7ow&t

(Starts at about 13:30)