My gf has a 03 monte carlo ss and I have a 04 monte Carlo Supercharged and her car does not start up easy like mine. I can turn key on mine and let go it starts up like a new car does. Her car you have to turn key over and hold it then it cranks . new battery alternator and new ignition spark plugs and wires fuel pump. If you try to start hers like mine it will make light coughing noise and chock out. Like I said if you hold key it doesn't cough it starts fine. It doesn't do like a weak battery does.

 

check fuel pressure, change the fuel filter, if #s low then try areplacement, fuel pressure regulator if #s still low, then get a fuel injector cleaning. You can also check voltage going to starter to see if it registers 12v when you turn the key to start, if not then you have a wiring, ignition switch/cylinder, or bcm issue. If you get 12v, then the starter could use replacement in the near future. If it cranks but never starts it could be the ICM (which is easy to replace).