Its a 1999 Monte Carlo Z34, 3800 engine. The car turns over, has 42 PSI fuel pressure and has no stored codes. I have replaced the ignition module, all coils, wires, pluges, air and fuel filters. Before this, when the car was driven, it would sometimes buck hard then drive fine. Every once and a while it wouldn't start but then 10 minutes later it would start and run fine. What else should i check? If its the computer itsself is there a way to check that? thank you in advance for any help.

Well, you have already verified that you have fuel pressure. Now you need to verify 2 other things. 1, verify you are getting spark during crank. 2, verify you are getting fuel into the cylinders by removing a sparkplug and seeing if its wet. Once that is done, we can diagnose further.

sounds like crank pos sensor

yep, thats what it was. Crankshaft position sensor.

Yep, crank sensor. Clasic symptoms.