I ask about the PH because in the guide for the K-2006 test kit it says high PH level can lead to high pressure in the filter. How this works I don’t know but I glean that the PH level needs to be balanced.

As for proper filtering, the pressure should be around 10psi and the flow from the inlets should be fairly strong. My shallow end inlet blows all the way across my 20 foot wide pool. With the pump running it is impossible to put a fitting on the inlet fitting. Not scientific but you get the idea.

My gut feeling is the filter is clogged. I know you cleaned it already but I’d do it again. I know that filter is a bear to open with all those bolts but that’s all part of the pool game.
I opened mine one year when it was acting up and I will never forget the glorious green algae covering all my tubes.