If i'm playing up,down,up down for the picking pattern I can play the fragment very fast and clean fairly easily,
Strange how your pref is that you can play tighter & faster/cleaner starting on an up stroke
but when I try to practice the other way round(down,up) i find that I top out at a much lower speed.
20 mins each way picking exercise with the metronome at low speed bring up in 5/10 increments should help.
3 Notes or 4 chromatic passages if you desire.
3 given below.Down
, up, down: ^_v_^
, Down, Up: V_^_V (Your strong method)Find a good teacher they are gold dust.