Chevrolet Repair: P0300 1999 4.3 Nightmare, crank sensor, ac delco

Question
Hello. 30 years under the hood professionally, First time in an automotive forum. Got a tough one.
99 Silverado 4.3 VIN W 132K miles, well taken care of.
Symptom: A little rough at idle, not bad enough to set a specific cylinder misfire code. Maybe one miss every 2 - 5 minutes on the road at highway speed. Very strong acceleration from a stop to 80 MPH, no missing.
My Genisys misfire counter shows the #1 and #4 cylinders are acting up the most.
The shop before me installed:
Cap, rotor, wires, coil, AC Delco Plugs, crank sensor.
After double checking their work, I installed a replacement spider, (happened to have an extra) with new regulator, no change.
I pulled the distributor, found the gear worn, replaced. Did the cam/crank sync procedure. No change.
Friday I replaced the ECM with a Napa Reman, flashed it in house, no change except a new torque convertor circuit problem, reinstalled the old ecm, verified the TC circuit problem was gone, and shipped back the defective "new one" .
Map, Maf, Tps, Cts sensors all look normal. Cam and Crank sensors look good on my Vantage Scope. I blocked the EGR off to make sure no leak there.
On startup, the CMP shows 0 on the scanner, after revving engine, defaults to -12 or -13.
Fuel pressure KOEO 60 psi. Running down the road, 54-62 psi.
Do you have any ideas? Thanks, Joe

Answer
Hi Joe,
Have you connected a vacuum guage and watched it.
Sounds like what an engine with worn valve guides might do when a valve occasionally doesn't hit the seat perfectly.
May not show up in a compression test, but a good vacuum guage might fluctuate.

Van