Loss of power and plenty of Dash Lights

I can be driving my Iszu Hombre 1998 rebuilt motor that I purchased in April it is a 5-Speed and I can be driving along in 5th gear and the Oil Pressure will drop below 40 and all light on the Dash will come on and I lose power…The ABS light will stay on until I restart the engine…I have it checked out and was said that it was the Crank-Shaft sensor have had it replaced because the diagnostic machine indicated it was bad…After replacing the sensor every so often …once every two weeks it does this momentarily and then runs fine but the oil pressure does not get ovr 60 and it runs near 64 or 65 when this is not happening