i have a 1991 z28 with a 5.7. ive been building the car for almost 2 years and it always ran fine. 2 weeks ago it refused to start and only the starter would go off. replaced the ecm, distributor, and plug wires. now it starts most of the time, but sometimes it still wont start. when it does start the idle is very rough and sometimes stall when put into gear. any opinions on how to fix this. thanks!

Have you checked your fuel pressure?

Check your ignition control module under the distributor cap. Take it to oreillys or autozone and let them check it on their machine. could be That. I've had the same issue with my 91 z28 before.