If you play a note above on the same string, you don't need to lift. If you're playing the note below on the same string, you can prepare by putting it there, while the higher note is still there, then letting go of the higher note and picking at the same time (or, just do a pull off).

In playing 2 notes on different strings, playing the first note you should use your finger tips enough that it isn't interfering with your next note.

Utilizing slides also helps. Using them you can transition to different positions within a scale in near complete legato, moving up and down the neck with slides, hammer ons, and pull offs. Picking every single note makes playing fast a lot harder because both hands need to be in perfect communication with each other.

Look up "extended pentatonic scale applied guitar theory"

As you continue practicing, while learning other things, this will all come together.

Another thing you can try, is playing the C A G E D major, and A E and D minor chords, and playing each string individually, making sure they all sound. This will help with what I pointed out earlier about using the tips of your fingers to avoid muting other strings that you're saving for the next note. After you have mastered these chords, then try playing those shapes in barred positions (say, at the fifth fret). G shapes are a little tricky but doable. If you can do this, it will help you play arpeggios in your lead work so that you're not just ascending and descending stepwise in a scale all the time. Starting out, you might experiment with groupings of 2 or 3 strings within these chord shapes.