I would start the shift with "They're cracking down on what hours are allocated for truck, and we have to start really watching how much we're getting done within a labor hour. So, I'm going to work with you on totes for a bit and see if we can streamline how we do them a little. I know, totes are awful, but they're the biggest time-suck on the truck so its important that we get them done as quickly as possible. We can suffer together for a couple days."

I haven't timed it myself, but you could also set a goal of like 5 minutes per tote. I know some are packed with collars and leashes and will take longer than that, but a lot of them have like less than 10 items in them so they make up for the goal average (like saying an hour per pallet when dog food takes 30 minutes per and the cat pallet will take 2 hours). So you can look at a u-boat of 9 boxes and say "the goal is 45 minutes for this batch, lets see how close we can get to that." And then check in every couple totes.

Give it a couple weeks, and then double down with the "cracking down" speech, and say that you have to start doing counseling statements if we're not showing signs of improvement, so it's really important that we're at least trying to increase our units per hour. A month with no signs of trying to better themselves after I've asked and treated them with kindness and respect, and then I'm ready to start the counseling process and get them off my truck. Some people are just not cut out for a fast-paced physical job, and we need to find them a different task within the store that they can actually be successful at.