1998 Chevy. Lumina Help Please!!

Any and all advise is truely reccomended!!
I have a 1998 Chevrolet Lumina 6 cylinder - 3.1 engine.
It is getting to the point that I am not sure how much further I am going to be able to go. It is surging .. From a cold start to going 65 mph down the highway. We replaced the fuel filter, that worked for a few days then its back, its surging - jerking so hard. When the engine is hot or cold it is doing it. Is there any way to pin point the problem or any one ever experiance this with some advice. My Chevy dealer charges $95 for a Dianostic service... I am on a VERY limited income and I would rather spend the $95 on the part and attempt to repair / replace what is necessary my self. Another way for me to describe how the car is acting would be to say imagine your self on a roler coaster chugging up the hill ... That is my car on flat land.

go to another gm dealer or a good mechenic and get it scanned while it is being driven, most gm dealers in my area do not charge the first time.

Sounds like possibly an injector that's bad. You'll need to get somebody to scan for codes to know for sure. Go to a place that'll do it for free and post the results.

Autozone will scan it for free.

We went to Auto Zone came up a Code P0300 They suggested replacing the Egnition Module but they did not have any in stock so we went to Advanced Auto and they suggested a Coil pack, Which we just tested all 3 and replaced one.. Running a LOT better but still a very little hesitation. So will probally replace the other 2 and hope for the best...