If the chip and ecm doesnt fix it.. then more than likely its the ignition module. Careful on the ignition module as aftermarket ones(Cardone,Wells,Etc) are known to exhibit issues. AC Delco's are the only ones that for sure work.
There are three parts I keep on the shelf for a Buick.
1) MAF stocker with BW sticker
2) Coil pack ignition module
3) Spare ECM + chip
If the three above parts are swapped and the car still has issues.. your in trouble
