The boost solenoid is out of circuit path during normal cranking. It simply provides a binding post for the 2 engine battery cables to join and continue. You cleaned "most" of your connections. Did you clean them witth something like Caig D5? You did not clean all of them and resistance in series is additve. You need to also load test your engine battery. I believe you have multiple problems contributing. Is your hot starting a no starter engagement or slow labored cranking. You don't actually clarrify. My 455 cranks faster than any GM car I have ever owned under all conditions and with a old starter.