A older van has only one ignition coil, if it were bad, all cylinders would misfire.
I suspect that it is not misfiring, but rather that the torque converter is skipping (shuddering is the official term). Does it feel like traveling over rumble strips? If so, change the ATF with a MERCON V fluid, and it should go away after a few hundred miles.
If not, look at the plugs or wires.