454 Chevy

I agree with the fuel filter issue, when the vehicle sits during a hot soak, it actually gets warmer as no air flow is going through the radiator, that can make fuel boil up to the carburetor or fuel injection thus making your vehicle run correctly. I would change the fuel filter first. Good luck.

Bob

My 454 carburerated has a fuel filter in the carb. Check that first.
Second 454s are notorious for collapsing the vacuum line to the distributor for vacuum advance.
My 454 was running like sh-t and my mechanic did all the vacuum lines. What a difference the truck runs great. Before I could hardly get up a hill.

Try these 2 simple cures first

Really need the year of the 454 carburetor, throttle body, port injected?

Just to many possibilities with out more information.

check the exhuast system.....the cat converter could be clogging up when it hot....

Sounds more like a clogged fuel filter to me..

I could have guessed your alternator has nothing to do with a 454 running badly.
Do a 'search' for 454 and you'll find a thread or two (well, I did) which might give you some help with your problem. Notice the comments about collapsed vacuum lines and distributor advance mechanisms. Don't discount the comments here about a failing fuel pump.

What year-- several different fuel systems used over the years?

Maybe the in-tank fuel pump is starting to fail. Check fuel pressure when cold and when hot.