Timing is fine, vac advance works fine.
8 BTDC, all in around 2.8k RPM @ 36 degrees.
This makes sense as like I said earlier:
If the truck idels a few minutes, punch it and accelerate moderately or WOT it's just fine for about 7 seconds and then stumbles almost completely stalls, let off the gas it recovers but if gas is re-applied it surges and won't accelerate or hold a speed properly.
The longer I stay off the gas the longer I can accelerate afterwards but it's back to surging pretty quickly. Timing isn't going to effect this.
It's a factory mechanical quadrajet with the correct timing.