[carnut]

The service manual talks about spark plug wires that can be too close to the HEI lead ins at the distributor causing an inductive miss. Also two cylinders side by side could be getting an inductive miss from the each others wires as well. Are the plug wires routed by the book and all in their respective retainers? I agree an EGR wont cause a miss at idle but you say its RPM related above idle. By verifying the miss with a timing light, describe what you see and how you arrive at that conclusion. Also this question regarding torque converter lock up can be verified by the orange icon in the climate panel as driven in diagnostics. Its either engaged or not by the lights illumination. Also 3 or 4 years after this year of car, there was a GM bulletin stating that a worn distributor drive gear could cause erratic performance. Something never looked at during diagnostics. There was an issue with dissimilar metals, camshaft to gear, causing the wear. An improved gear was issued to correct this.