Hayward Super pump has little intake pressure

Hello from a forum newbie
Up until yesterday, my Haward Super Pump moved my Navigator cleaner up walls and super fast. I changed the filtering basket since the old one was broken, and now, the pump pressure is very weak.
Observations:
1. Regardless of the valve open (suction, main, and skimmer), the pump's basket only fills up about halfway and the cartridge filter's pressure reading stays at 0.
2. The suction cleaner moves, but very slowly.
3. When I turn the pump off, a rush of water fills the pump's basket completely. The water comes from the return side.
4. I stuck my hand in the basket's hole that goes toward the pump's motor to clean it out as much as possible.
5. I took the pump apart, and the impeller looked clean.
6. The basket's lid is closed tight and free of debris; no water spits out when I turn the pump off.
7. I poured water on all pipes and valves but did not see any bubbles.
8. The water level is high above the skimmer line.

I suspect, perhaps, that something is blocking my pool cleaners intake line; that's the one I use the most.
Do i use a hose to send water backwards from the pump to the valves and lines to possibly loosen something stuck? What else can I try?

Thank you

16k gallon inground pool
Cartridge filter and 1.5hp Hayward Super pump
3 intakes (main, skimmer, suction)
3 returns