Well...a quick update.
I got my chemicals balanced out and now my pool is ultra clean and clear and looking perfect.
That being said, I'm still only using about 1/5 to 1/6 the recommended amount of DE.

Just to clarify, I have no problem with the water flow in terms of inlets, eyeballs, valves, etc. Everything is functioning totally fine as long as the filter pressure stays in the good range. Once I add more DE and the pressure rises, then the flow stops to a crawl.