What did they do to fix the problem? If you are able to do work to the car yourself, all of the things you mention are relatively easy to do. We will walk you through it if you want to try.

Do the work your self. There'* a write up on all that in tech info. O2 sensor, $40 or so, 30 to 60 mins depending on how hard it is to get the old one out. Fuel filter, about $10 and 30 mins of time. Plugs, about $10 for autolites and 30 to 60 mins of time. Injector clean, $8 for a can of seafoam. Total, about $70 and 2 or 3 hours total.

I pretty much have the same issue with my car a 99 bonneville. Just started this week the first few times it died it sputtered right before it died. But it only seemed to die when the engine was warm, after a little wait it will start back up. I had my buddy come over with his scanner and saw I had a bad crank sensor I replaced that. Took it for a drive and it died on me again when it was warm, but this time it was more like a switch and just died. I checked and cleaned the connection even checked for erosion on all the battery cables, all good. Everything like the plugs, wires, fuel filter are not even a year old. Alternator passed all tests at the auto store. Help please