Unhappy 360 (At idle)

Stephan D said

The sound of the video is a bit misleading, but the idle is approx. 750 RPM in Neutral and 650 RPM in gear, there is a timing label under the hood that says 10 degrees +- 2 degrees at 750 RPM.
The hose routing sticker is there as well but outdated as most of the emissions stuff is gone, our domestic emissions regulations are quite liberal for vintage cars, not so for current vehicles.

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Stephan, The drop of 100 rpm indicates the engine has less power at idle than it should. It's prob too lean and slightly advanced.
There could be a big difference between setting 15° and 10° at 750 rpm.
Try 12° at 750 in neutral/park. You may have to fiddle with the idle speed (throttle stop). Then turn the idle mix screws until lean drop off, and then make them 1/4 turn richer.

It will be useful to see exactly what emissions was on the truck, and still is on the truck. If it had EGR, that would not come into play at idle. If it still has EGR, it needs to be correctly hooked up or it will be open at the wrong times. Not hard to do. If theair injection check valve or tubes are leaking, that can slightly mess up the cylinder mixtures especially at low rpm. What happens the exhaust leaving the the cylinder runs into near atmospheric pressure.