Random Missfire Problem!!

Hey, I'm new to this forum, but i have a 91 cavalier and just started noticing a big problem. It randomly starts missfiring on 1-2 cylinders! I've replaced plugs, wires, coils, and cleaned the carb, but the problem persists. Any help would be much appreciated. I've heard that it could possible be the head gasket, which can be a pricey replacement, but i'm hoping that's not the problem.
Thanks,
DAVE