Yea, the Hayward S244T design sucks -- the sand bed depth is too shallow. 15 GPM / sft is optimistic on that filter; 20 is ridiculous. Your filter pressures would be OK if everything else is, but if the sand's mostly gone, you'd get those low pressures just because there's nothing there to create resistance.

The good news is that it's really easy to work on, just tedious with all those bolts.

Your pump performance is determined by the pump, not the motor -- you need the pump M/N rather than the motor M/N