I have a 1996 chevy s-10 pick-up 4.3l vin x automatic. I turn the key wait for the fuel pump to stop and turn the key to start, the engine cranks but does not start right then, i turn the key off again and back to cranking it will start up then. After that the engine runs great. All sensors were replaced, 3 days ago for another problem. We have correct fuel pressure at fuel check point.What could be wrong.