Have you checked ignition timing yet?
Alternators only put out as much as the electrical system demands. You can run a 200-amp unit but if your electrical accessories only pull 40 amps that's all it'll ever put out. What's the voltage when running?
There is more diagnosis you should be doing with tools instead of "this part might be an issue, replace". All you need to do to check whether it needs a voltage regulator is to use a multimeter and measure the voltage across the battery terminals or from alt output to ground while the engine is running. If it's over 14.5V (ideally lower due to your ambient temps), that's a problem.
If the fuel is indeed boiling, the engine should still at least try to start and run to some degree. If it's not firing at all that points more to ignition issues.
I'm not sure why folks are assuming I'm going at this as "this might be an issue, replace"; I'm going at this on a "do research, ask questions, get feedback, start working on the things that would be beneficial even if it's not the exact problem, test, continue".
If fuel is boiling, that's a problem, so might as well do something about it. If it's
not a problem (or not "the" problem), then doing something to make sure it doesn't become a problem isn't exactly a bad thing, and it rules out one potential issue. I know I don't know much about motors or diagnostics, so as I'm doing more research I'm asking questions. Asking questions does not equal just running out and replacing things. To your questions:
I have not checked the timing yet. I just got the last part for the fuel lines last night so hope to finish that up today.
I tested the alternator with a multimeter and it's fine; it's showing 14 on the gauge and similar at the battery. The old alternator was definitely not charging as I tested it the same way. Again, I keep coming back to the alternator because the problems started immediately after I replaced it, and that was the only change that was made. Still, I totally understand that one does not necessarily equal the other.
The engine does not start at all after it dies. It turns over very strongly but will not start for a solid 2 hours after the fact. After this most recent failure it wouldn't start for well over two hours; I ended up pushing it back into the garage and starting it the next morning, though it took quite a pull on the starter before it fired.
Ultimately I think under hood
heat is the ultimate cause, but since the car has gotten hot before I think it's affecting some other part. Someone had suggested the coil before, and it sounds like you might be in agreement with that possibility.
