Going from 20-50 to 10-30 will make a difference. But not a 30-40 PSI difference. I use a 1/2 drill and 2 hands to spin the pump with authority while priming. If you're spinning the pump easily with a 3/8, something's fishy. Wide open with an 800 RPM 1/2 drill should get 60-70 PSI and running the drill slow maybe 30. If not, I would try another filter for the heck of it before looking deeper.