The tremolo. Note the RH fingering I suggest. Although a very few guitarists play that as PIMA, classical guitar instructors since Francisco Tarrega, the father of modern classical guitar technique, have claimed it is much easier to maintain a steady rhythm with PAMI. With PIMA there is a tendency to "gallop". If this is difficult, I suggest isolating this exercise and changing the tempo to about 60 bpm. Play it at that speed for two weeks. Don't cheat or give yourself a progress report, but instead, play this very slowly for 15 minutes a day. Your goals is to program your subconscious. Cheating defeats the programming. At the end of two weeks, guaranteed, you'll have a fine tremolo.