I'm not sure of the reasons behind your undying loyalty to Costco gasoline. I think that point that I, and many others were trying to make, is that maybe, JUST MAYBE Costco had put out some bad/contaminated gasoline. An easy and relatively cost effective way to test that theory would be to try some different gasoline for a tank or two. Preferably Shell, BP, or Mobil.
Lastly, without seeing the engine data during the occurrence (perceived knocking) you have no idea WHY it is knocking. If you are not seeing any engine codes to assist in your diagnosis of the problem, logging will be the best way to do this. Other than gasoline octane, things to consider would be running lean due to improper air / fuel mixing (air leak or fuel blockage), improper timing, compression ratio change due to carbon buildup in the cylinder or too thin head gasket, fouled
spark plugs, or a bad knock sensor. Almost all of these could be evaluated via logging or cursory inspection of the affected hardware.