I'm not sure regarding the secondary diaphram. I'm assuming you're referring to the "Depression Chamber"?

I did replace the filter last Thursday just to cover my bases. It actually seemed to help SOME. But going up hills at speed (throttle mostly wide open) it begins to make the pinging/rattling sound. If I pull off to the side, and let it idle for a minute or two, then jump back on, it seems to recover.

I'm in agreement with you both, as I believe this to be a lean condition, more so than a timing issue. It's time to take a closer look at my pump and carb. I was needing a good excuse to get a weber anyway..