When you have a problem with a particular technique , overpractice it , give it some focusing , and you'll get it.

Probably 3-strings sweeps are easy to me cuz when I began sweeping I was 100% focusing on them.

Kirk Hammett's solo intro from "lepper messiah" & malmsteen diminished 3-string sweeps are good examples to practice... Those were the first sweeps I've ever learned.