So fast forward to now, I've ditched the Costco pacs; gave the half tub to our neighbor because they could care less how the machine is working (they've replaced their dishwasher twice since we've lived here and they've all been the cheapest contractor-special WPs and GEs you can buy). I went and bought a small thing of Cascade Complete pacs, because in all my years using and owning dishwashers, I've never had a complaint or issue with their pac based detergents, other than Platinum seeming a bit overkill and sudsing, and I've now run 4 full cycles with this machine without any issue. The upper arm sounds just as perky and spry as it's always been.
Until just today, I had about a half load of dishes that needed to just go ahead and run, because we've been busy and I don't want dirty dishes sitting more than a couple of days and smelling rank, and I decided to try using a half dispenser dose of the Great Value powder I've had in an air tight container to use as occasional prewash and to soak really stubborn pots or baking dishes in the sink. I'll be d*mned if I'm not sitting at the kitchen table working through bills and listening to the dishwasher and the upper arm starts the same gradual slowdown and finally stops. It took three wash level changes to finally get the arm to slowly start rotating again and back to normal. During any of this, the lower arm, the upper spinner, and the spray tubes all rotate just fine.
Two things I will add that I've tried with this situation so far:
1. The upper arm assembly on this new platform does NOT come apart. I have to say, the GlobalWash did it best with the easy quarter-turn locking nuts on both arms. On this new design, the lower comes out easily with a counterclockwise turn, but the upper seems permanently installed. I've tried tightening the center hub where the metal arm meets the plastic center, and it'll move barely, but I'm not sure it's doing anything because I have no clue if it's even threaded, or just a snap in, and I'm scared to force anything for fear of breaking and ruining the whole manifold. That said, "tightening" it seemed to help slightly with the blow-by of water from the center, but not that much. This is definitely a disappointment for me with Whirlpool, one for taking a step back with no way to easily remove the upper arm, and two for the amount of spewing from the center hub. The GlobalWash design was far superior with very minimal leaking.
2. I tried swapping in the Whirlpool version upper arm, because these arm and manifold assemblies do easily unlock from the rack. The plastic arm also doesn't have the issue of the metal one where there's a plastic-to-metal connection; it seems to be just the arm connected into the supply manifold. I'm unsure if either arm design has any sort of nylon bearing inside to help with rotation and sealing.
Anyway, the plastic arm did the SAME THING. Did just fine rotating until the detergent dispensed, and slowed to a stop. Again, no pressure drop, no sudslocking, nothing. No change in motor sound or speed.
So my official conclusion with all of this is that I'm officially done with any generic branded detergents, even as "nice" as Costco or Sam's makes their brand pacs to be. There's obviously something in them, be it just cheaper ingredients or some kind of very microscopically fine silt they use as filler for weight, but it's obviously causing some kind of friction in this wash arm's center hub, and if it's doing this to the wash arm, what is it also doing to my motor seals and diverter? It's even more evident given that with the Cascade Complete pacs, even the first wash made a night and day difference in the sound and rotation of all three wash arms, along with having no residues to speak of on the machine's tub surfaces.
I'm sure Technology Connections would hate me saying this after his videos about dishwasher pacs on Youtube, but I have to disagree that the cheaper detergents work "just as well" as the brand names. There's obviously something in those pretty Cascade colors that not only cleans and shines better, but is better for the machine's health as well.