Hi Mike,
Why do you think it's your distributor? Had any other issues lately that might cause you to think that's at fault? I wouldn't guess a dizzy shaft would wear out like that, or result in that kind of problem (and runs fine above 3K...)
My own initial-hunches based upon the symptoms you've described are: Bad gas? Carb cleaning, or a clogged fuel filter or maybe jet? Fuel pump? (or something related to the recent high-temps we're having here? Like possibly vapor-lock?)
I wouldn't come up with a dizzy-specific culprit until after checking out stuff like fuel first. Then I'd look at spark - coil, plugs condition, etc. It sounds like this missing came from out of nowhere, unrelated to anything you might have recently tweaked on your car, right?
If it was something with the dizzy, maybe it's evident from looking at any cap-wear you might have or what the rotor looks like? (If you have a worn dist-shaft it seems you might see starnge wear on those parts.) Maybe you threw or have a worn advance spring issue? BTW, you don't have points any longer, right? otherwise that would be a good guess too...
Sorry to not be of much direct help on your question - and that these ideas might be helpful to you solving your problem.
Tom