Q: What should of been a simple fix, has turned out to be a much more and in depth diagnosis of my 2000 Chevy Impala

I have a 2000 Chevy Impala for 5 years and this is the first time that I've had issues with the car. I've had 3 different mechanics tell me whats wrong with my car. My ignition switch, the starter, the battery, the alternator, and the fuel pump. I've lost hope in rying to find someone to get my car up and ready for fear that I will get a fourth opinion that' different. I have been doing research on my own and I feel it could be the crankshaft sensor. I'm not sure but I wanted to know what the difference between the crankshaft and the camshaft is and what would the symptoms look like? Im running out of options so opinion is what considering. Thank you. By replacing all of those things mentioned above it has not enhanced the car cars performance. In fact the car doesn't always start. It drives rough and there's no speed and I need that speed. No freeway either.
My car has an automatic transmission.