New MM, I need help

I just became the mm at my store a month or two ago, and I’m constantly struggling to hit box count. I’ve seen other mm on here say that they can get 200+ out in one 8 hr shift and I know by DT productivity standards that makes sense because my stockers only come for part time shifts but get around 100 still. It feels like it’s either that our flows are messed up which they really are, or that we legit have too much stock for the shelves. Our old mm left the back room pretty full so it’s up to me and the team now of course, to fix up EVERYTHING before inventory soon. How can I start getting more boxes out? I do everything else as a manager perfectly, I just feel like I’m lacking at the most important part of my job and it feels terrible.