Down 84 pounds in a year, now grinding through a flat stretch

I hit my one-year mark this week. Down 84 lbs from my highest, but since early August I've bounced inside a 3-lb range. I still track protein, walk 30 minutes after lunch, and lift twice a week. Sleep has been mediocre. Appetite suppression isn't as loud, but food noise is creeping back at night. I'm not quitting. I'm just bored and annoyed by the flat line. For those who hit a months-long plateau after a big loss, what did you change first: calories, training, sleep, or just waiting it out?