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Random Misfire

Hello all. I hope some out there has a few suggestions to my random problem. My 95 chevy 1500 5.7/350 with 40,000 on new crate motor is misfiring randomly.

For the past few months, it would misfire sporadically while sitting at a light and in gear after about 20-30 seconds. Do not notice any issues while in park (RPM change may solve the issue) or while driving. Now that it is below freezing in the mornings, it is misfiring constantly during the initial warmup (in gear and sitting at stop light) and only misfires randomly after a few miles of driving and stoped at at light.

I have replace almost every sensor recently (cts (2), egr and solenoid (from Dealer), O2, Fuel pump and regulator, Fuel Filter, PVC Valve, Coil, ignition module, and injectors. In addition, I did a complete tune up with 2 differnt sets of plugs, 2 caps, 2 rotors, and wires. Have checked for vacuum leaks, and there are no codes. Timing is spot on. I took it to my mechanic and it has them stumped as well.

I am really stressing about this since I know it is not right. I was going to replace the pick-up coil in the distributor next and check for vacuum leaks while it is cold (Manifold issue?). Weird thing is that it runs really well while driving with no noticeable misfire and I am getting 13 mpg in town. Any help would be greatly appreciated. Thanks