When you are having trouble with one aspect of something, you need to isolate theproblem and practice it repetatively. If you are having trouble with pull-offs just practice that. Practice scales and modes using only pull-offs. I presume that your ring finger and pinkie are what is giving you the most trouble. (I am a guitar/music instructor and this is very common.) Just practice pull-offs between those two fingers. Start with a half step pull-off then move to whole step and furthur if you feel comfortable with it.