I just replaced the plugs two weeks (or less than 100 miles) ago, and the old ones were actually not bad at all. I used the ones y'all always recommend (Champion?).
Battery and voltage regulator are about a month old and alternator tested fine two weeks ago (when I went to AZ to check that new battery and voltage reg had solved my starting problem).
To clarify, the car is not dying at all. It starts, and drives fine except for the occasional pinging/straining when accelerating up hills that I used to associate with bad gas or, well, all the cars I drove in the 70s and 80s

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What happens is if I turn it off after driving a bit and try to start it soon after stopping it (most recently it was after filling up with gas), it acts like the battery is dead. Meaning it has almost no power on crank, the dash lights dim, and it doesn't turn over. Wait fifteen minutes and it starts right up.
My other car that has suddenly developed this same exact problem is a 1970 Chevy El Camino I just got back from months at a shop (old guy working very slowly on old cars). I drove it home 70 miles with no problem, but now it IS having a hard time idling now and does die. If it dies when cold, no problem, it will start right up. If it dies hot, I have to wait in the same way I wait for the Le Baron.
Both cars did this last night, since I specifically tested them both by driving them and then trying to start them up again when I got safely home. Same acting like the battery is dead on crank. Same starting right up when I tried an hour later. Since they are very different cars (El Camino has practically nothing electronic), I can eliminate a lot of things and thus assumed it might be a common problem I'm not thinking of. Or, of course, it's just a coincidence.