Why is it hard to start when hot?

the ECU shuts down all cars (cruise controls) if ECM or TCM sees hard errors, for safety and by law. even brake lamps dead. and more.
never put additives in the gas tank ever, for sure Marvel mystery Oil ever or wreck the injectors you will, a horrible act.
lost power is normal on overheating engines. (cause and effect)
the engine needs service, like 99% of all 26 year old cars.
It will; have lots of problems is not serviced regularly.
USA car?
back in 1996 ECU only some simple checks by ECU then OBD2 USA./
it is just basics not a very smart, Check engine light*(CEL)
In Canada, the ECU is even more DDummbb(sic) this year.

check oil levels at every fuel fill up, on 26 year old engines.( for sure)
that old the joke is
"stop at the Station,and fill up oil, and after check fuel too if needed."

do not drive cars based on dash lamps, do the checks your self
even look for coolant leaks hood up hot engine,
check for belts frayed or loose or missing
check for brake fluid leaks, all corners and master cylinder , levels good.
make sure you run 50% Antifreeze for engine coolant, fresh is best.
not pure water, ever, or it will boil over , for sure.

yes it needs service, nobody here can look under the hood and test things, using real tools. (in a text box) but can say get it serviced.
with real coolant. the boil point is 265F, so if you ever hear or see it boil, you now that is a hard failure and to not drive it but stop and fix it. or damage can go worse warping head or block or worse.
at this ages, most hoses here are totally EOL , end of life)
and the thermostat too.(or more)

check other thread just posted

I’m happy to help further over the phone at https://www.6ya.com/expert/john_5260ce46f2f674cc

check coolant temperature sensor

auto shutoff relay faulty..

runs perfect all the time hot engine, even up hills?
ever do a tuneup
do the 60,000 mile service points? or the 90?
bad running engines, do not want to start.
did you try the 2 tricks in the operators guide
1: crank with 10% throttle (helps finding stuck closed ISC valve)
2: crank it W.O.T? clears the flooding.

got idle problems , hot engine? too low, too high>? key symptoms.
got misfire up hills,
is the CEL glowing running > Check engine lamp
ever scan it? see if DTCs are stored??????????????????????????

Number 1: get the code; even if they light turns off an on, the code will be stored in the computer.

It sounds like you could have a variety of issues and more information needs to be given. How is the car running? Does it run & idle perfectly or does it stumble?

cheak fluid

You need to run a fault code test.

yes, run scanner for trouble codes

sounds like a dodgy mis reading of a sensor caused by electrical resistance which is turning choke on and flooding engine.know the fault but without car in front of me its difficult to diagnose,could be auto choke sensor which is on right hand side of cylinder head ,but not sure.best is probally dealer have you tried spark plug gaps ??25th although this would cause problems with cold starting not hot starting but its worth a look