Keeps shutting off put new alternator, voltage regulator and fuel filter will run for about 20 mins then just shuts off sometimes it sputters most of the time it just shuts off like turning off a switch

Likely you are draining the battery with your system use during the car operating. This drag down of the battery means that your alternator may not be working properly. Check the alternator to see if it is putting out voltage. Otherwise check the battery during operation to see a higher voltage on the terminals if it is getting charge from the alternator.

i am not sure but it is possible that the engine shuts off when the alternator puts out more voltage than it should ( to save the computor or a fire) ... 13 to 15vdc max
you may have a bad alternator or voltage regulator.

check make sure alternator charging battery bad alternator will cause PCM problems since PCM brain of the car.have alternator voltage out put checked should be 13.5 - 14.5 volts.if you see 11.0 volts or lower alternator failing.

Almost sound's like vapor lock , the fuel boils in the fuel injector rail , turns to vapor ! That was a common problem with carburetors , letting the vehicle hot soak after shutting down the vehicle an letting it sit for 10- 15 mins. The fuel would boil away ! Are the cooling fans working ? After turning off a hot engine the cooling fans can run on without the key being on , do you hear fans run ? What engine does your impala have ? 3.4 or 3.8 L . Has the check engine light come on ? The fuel pressure regulator could be leaking fuel . Pull the vacuum hose off the regulator after shut off the vehicle , is there fuel coming out of the regulator ? Dribbling out the end of the hose ? This could be bleeding the fuel from the fuel rail ! Good luck , hope i've given you something's to check that you haven't already .

(this is for others who may be viewing this problem)
P1594 = charging system voltage is too high
P0320 = crankshaft position sensor (CKP)/engine speed (RPM) sensor-circuit malfunction
P0463 = fuel level sensor circuit, high output
P1391 = intermittent loss of CMP (camshaft position) or CKP (crank position) sensor

Probably start with changing the crank sensor. But keep in mind that the high charging system voltage may be causing the other electrical sensor problems. The voltage regulator (probably located internally in the alternator) is not regulating voltage properly. So changing the alternator may be needed as well. Price the parts and start with replacing the less expensive first.

Have your alternator checked, the voltage regulator which is an internal part in your alternator may be going bad and when there is an electrical load. The alternator does not produce enough voltage. That a multi meter and check your voltage at the battery, engine not running you should have 11.5 to 12 volts.
With the engine running you should have 13.5 to 14.0 volt reading at the battery, turn on your A/C blowers on high and head lights on and you should still have a minimum of 13.5 volts at the battery.
If your readings drops less then 10 volts, the Bravade ECM will shut down the fuel pump or the voltage is to low for the electric fuel pump to keep the fuel pressure at 56 PSI which will cause the fuel injectors to stop working.
Thank you or using fixya and good luck.

Do you have any of you fuel lines close to the exhaust? (vapor lock)

Try changing your fuel filter. And take a fuel pressure test.

Nothing wrong with the regulator. That is how it is supposed to work, it sounds normal.
I guess you will have to get to the spider to see what is wrong. Fuel delivery to the pot seems normal. Could be something to do with injector circuit, IDK. Sorry can't help more.

Possible fuel filter, fuel pressure regulator. fuel injector