Detonation...yeah I never thought of that! I filled it up at a Safeway gas station last, but I've taken it there before. I reset the timing about a year ago, but I've never checked the points in as long as I've had the truck. I don't know anything about points...what should I be checking for? What do I do? And the vacuum advance, that's in the distributor isn't it? The whole distributor moves when the engine is revved.

Yeah that noise shows up only under load, not when idling or revved.