[Steeveedee]

As old as the truck is, it is entirely possible that the harmonic balancer elastomeric ring has allowed the outer metal ring to slip. When this happens, you have an apparent advance in the timing mark on that ring. You will have to determine where TDC actually is, and compensate for that. The fact that you are running well at 22° "base" timing is a potential indication. If it isn't pinging at that setting, leave it for now. Were it mine, I'd be for verifying that the balancer is OK. Two reasons- next time you take it to a shop and they adjust the timing, you'll be back to square 1; secondly, if that ring is actually deteriorated, the outer steel ring can fall off. Bad to worse, I'd say. I'm not claiming that the balancer has slipped, I'm only pointing to a possibility.

I worked as a SMOG mechanic for many years, and we'd get vehicles rejected from the test-only stations because of "over-advanced" timing. We'd have to diagnose it correctly and send the customer back with information indicating that the balancer had slipped. I always recommended they get it fixed, and if they had a favorite mechanic (not all of them had a SMOG license), they could take it there. I'm not one of those guys who sold them the parts and labor before I signed the paperwork off.