My car dies out constantly..usually when i slow down or come to a stop..i have replaced the alt. The fuel filter and back o2 sensor..i have tried gas treatments..i am stumped as to what the prob could be..i have also had it put on a machine to look for codes...there were no codes seen by the mechanic...help!!!

alt died
then in 30min driving the battery dies and engine stops
the engine run off the ALT full time until the ALT dies
causing rapid battery discharge. and engine stalls.

do not replace the alternator with battery NEG lug connected of blow up ALT FUSES, never fun that.
or on newer smarter alts , it shuts down if 1 battery cell of 6 goes open or shorts, this prevents battery explosion.
so we load test the battery first. then if good the alt is bad. or we test the alt next.
this failure is super common , for 100 years.
we test the both carefully

the alt good will put 13v to 15vdc on the 2 battery lugs.
even at idle, and any dmm meter made can see that.

Fault codes would help, but based on the fault description You probably need your throttle body cleaned and basic setting carried out on throttle.

Spark plugs or injecters are clogged.

sounds like the alternator has quit charging,,try a jump start and check voltage at the battery after it starts (cables off)
(If it dies after the cables are unhooked ,the alt. is bad.)

Get the codes read to find out why the engine warning light is on

yes there is a pump in the tank and it sounds like that is the problem

you maybe running a slow idle speed. When the alt kicks in to charge the battery- your engine may slow down to the point it dies from speed issues, or because the over all voltage available to the solid state ignition goes below 9volts. (it's minimum requirement to fire)

check tps sensor (throttle position sensor in backside of the throttle cable) and map sensor (manifold absolute pressure on front little 1 inch sensor with vacuum line) make sure there plugged in. the ecm (engine control module driver side inner fender) and tcm (transmission control module under dash) both need the data to know when to upshift and increase fuel/air. Otherwise the computer runs default values and guesses off of other sensors giving poor performance. also disconnect battery for 15 min. usually resets aveo service lights if you dont have a scanner.

replace your pcv valve

the alt is not working right re place alt