I have a 2003 Silverado 4.3. I've been getting intermittent start no starts. I've changed the plugs,cap and rotor, tested the ignition module and coil. I've also cleaned up the body grounds and removed the crank sensor and cleaned it. It has me baffled. Please help.

Welcome to the forums!
When it did not start were there any engine lights on dash etc?
Have you scanned for any history/stored codes?
Generally the place to start is from the battery, load test it to ensure it is good.
Next make sure all the battery cables/connections are clean, free from corrosion & tight.
The security may also cause issues like this as well as ignition.
You can Google 2003 Silverado intermittent start, you are not alone in problems unfortunately.