If you turn power off to the pump and let it sit does the pressure hold constant? I believe you have said it does in your comments. Next if there is a shut-off on the piping going to the house turn it off. The pressure switch and gauge must be on the pump side of the valve not house side. Turn the power back on and then see if your pump will build pressure up to turn the switch off. Since you have turned the adjusting screws for the switch watch the pressure gauge closely and if it gets above 70psi kill the power. With the system isolated if the pump can not build pressure then you are right and it should be replaced.