2003 Oldsmobile Alero help!

It's NEVER a good idea to replace parts until you get lucky and cure a problem. That dealer who has been advising you is a complete idiot.

Now, does you check engine light come on when you car dies? If so, have your computer scanned for codes. This'll point you in the right direction. (If the computer says, example "O2 circuit fault", that doesn't mean replace the O2 sensor. It's only pointing you in a direction so you can check that system until you find the fault)

I suggest testing the crankshaft/camshaft positioning sensors. Again, check for proper operation before replacing.