Changing the motor out of the Fadal pump will not change the effective GPM of the pump.
Possibilities are - The motor as lacking in power and stalling out.
- The motor is the wrong RPM.
- Nothing wrong with the motor but the pump is wore out.
I don't know about your area but here that motor would cost me less than $150 to replace and likely be repairable at my local motor shop for under $60.