Problem keeping good form on this

[Mateo150]

I've been trying to learn this piece for a while, I can play it, but not cleanly. In particular, this passage is giving me lots of problems. Please look at the powertab, one thing is the on the hammer on /pull offs that I need to do while my thumb is playing the bass note. My pinky tends to raise way off the fretboard because it straightens out, it doesn't do this when my thumb isn't playing the bass note. I play so that my pinky's fingernail is adjacent to my ring fingers fingernail, and I often try to keep these two fingers together and use them as one finger. When playing some of the phases, in particular measure 3, my pinky does not maintain postition when playing it in speed. Any ideas how to improve this, I can play slower and focus on trying to keep the pinky in position, but is there anything else that works for this type of problem?