Quoting these to get some input here - Just had a 7" Maxtrac lift installed on my RWD 2021. I also have the 6'4" bed, and the 2-piece drive shaft. When I ordered the kit, there wasn't an option for the carrier bearing drop/spacer kit (so I had no idea it was even a thing). After the lift was installed a couple days ago, I now have some vibration between 52-58 mph, that I never had before, so started researching, and found out about this. I emailed Maxtrac, and they said it wasn't offered, because it's not needed for the 2019 and newer models... But, looks like other manufacturers sell it, as per what you guys are saying. If BDS has it (and their "sister" company, Zone, sells it for the 2021 model).
So - Is it necessary? For $40-$50, I'll get it, looks easy enough to put on myself. No harm, right?