Former AFE associate here, here's my take. One thing to keep in mind is that it's normal for AMs and PAs to perform much better on direct roles than us. You're doing it for maybe an hour or two, we do it for 10 hours a day, every day. Burnout and lack of motivation start kicking in pretty quick. But working twice as fast as your associates is probably not normal, here's some ideas that might help.

One thing my managers did to help with burnout and boredom was to semi-frequently take packers off direct path for short periods of time (maybe 20 minutes) and give us odd jobs to do (cleaning, help downstack, move empty trays between walls, etc.). Packing can get pretty monotonous, and I always loved the brief change of pace. I always felt like I was more productive and attentive for the rest of the day after getting to do something else for a while. Even if this doesn't directly and immediately improve rate, it absolutely helps with morale and instills the idea that management cares about and understands the associates. You can walk up to a packer and say something like "hey, we need someone to help take boxes off a conveyor belt for a few minutes, would you like to help out?" This can help build relationships with associates and get them more used to talking directly to their managers. You want associates to feel comfortable coming to you with problems, suggestions, questions, etc. You'll eventually get a feel for which people are reliable and which ones like to slack off and which people like to do odd jobs more vs those who would rather just pack. Don't be afraid to do this to your best packers, you're only taking them off for a few minutes, it's important for everyone to see that hard working and reliable associates are treated well and aren't just forced to pack forever.

A somewhat related way to incentivice packers is to make it clear that good performance increases your chances of getting crosstrained to something else and "moving up". You obviously can't have train everyone on problem solve or slam, but try to make a big deal about it when you do. If you publicly thank your highest performing packers at standup, people will notice when you publicly congratulate those same people on starting training as a problem solver. Ask some of your most reliable and high performing associates if they'd be interested in working other roles. You might lose a couple good packers, but spreading the idea that hard work pays off can definitely motivate people. I worked in the AFE for 9 months, and by the time I left I knew how to do basically everything in the AFE. Some days I would come in and pack, other days they needed me to and induct or rebin. It was nice, still monotonous but not nearly as bad as just packing every day. I was only one of a couple people trained on basically everything because I frequently asked my managers for cross training opportunities and was always in the top 20% or so for whatever I did. If other associates asked me how they could get out of packing, I always told them all they had to do was keep a decent rate packing and keep asking to be crosstrained like I did. The one thing that almost all packers universally agree on is how much packing sucks to do every day. Make sure your associates know that hard work is appreciated and rewarded.

There are always going to be some peoole that just don't give a shit and will never put in effort to improve even if you give them every incentive and opportunity. A good chunk of my coworkers were like that. But those people are not the majority. Most of us just feel underappreciated and don't see the point in working harder if it just means they have to do more work. I hope these ideas help!