Service Engine Soon Light with New Plugs

I have a 2000 Alero with 101k miles. I got in the other day after a stop at a gas station and it started to shake excessively under the hood. I turned it off and it did the same thing again. On the way home the SES light started flashing red. I had the code read and it gave a "Multiple Cylinder Misfire" readout. I replaced the wires and spark plugs and now it seems to continue to vibrate when taken out of park or with the A/C on in park. Oh yeah, now the SES light is yellow and flashing. Any help would be appreciated.

Sounds like you may have a bad coil pack.

Thanks. I took it to a dealer this morning and that is what they said. Thanks for the input but it's about $50 too late. I'll let you know how it turns out.