Sounds like the overheat switch inside the pump is tripping. They reset after a few minutes typically.
Until you find the cause, try turning down the pressure, perhaps 25 to 40.
A quick diagnostic is to check the running amps and compare it to the motor specs. Then check the wires for leakage to ground. Sounds like the pump is getting tired.
Do a search for Franklin electrics AIM manual. It explains all.