could be a fould plug a loose plug wire faulty coil fualty coil conection
basically start with the easiest
make sure wires are all connected securley, plugs arent damaged
you can test the ohms on the wires you will need a basic multi metter they sell at sears for around 20 bucks
Honestly it gets frustrating diagnoising problems like that so good luck
gpona.com has a gm service manual link on it maybe that might help you out