1987 z28 Camaro has starting problems

I have a 1987 iroc z28 with a 305 v8 4bbl . I have changed out: Starter and solenoid, Alternator,rotor,distributor cap, spark plugs and cables. i replaced gas filter. The night we put in the new starter the car started up fine and immediately and we drove it for about 30minutes. The next morning the car wouldn't start. So we changed the alternator which needed to be replaced since it was only giving out 5volts. The car started fine. We parked and came back a couple of hours later to start the car again. The engine turns but it turns slowly and then faster and then slow, but doesn't start. I have inspected the flywheel and it looks fine also(no signs of wear and tear). After cranking it several times and giving it gas the car starts...eventually!What else can i look for or any recommendations. I have run out of ideals...
-Thanks-
17yr old girl and dad

So it has trouble turning over and firing, but it runs fine once you get it started?

yeah, it works fine once you get it started, but it just doesn't want to start initially....