'89 cutlass supreme having some issues

hi,
i bought a 89 cutlass supreme sl v6 2.8l and it ran like a dream no problems once so every. i made the choice to take a long trip in it and it broke down(wouldnt start) and i had no other choice but to take it to a pep boys and since i got it back it has ran horrible. i would like to kno if anyone has any info. they replaced these parts:

1) crankshaft position sensor
2) ignition control mod/unit bwd control module

and on top of this i had my fuel filter changed.....since then the car has stalled a few times and when u throw it in reverse the whole car shakes like crazy....if anyone has any clue what is up with that please give me some ideas. thanx

Does your vehicle have a Electronic Spark Control module or similiar? I had a vehicle that had a bad one and it acted similiar but, my check engine light would come on after it started to act up, then go off. maybe that will help