Strange Missfire
 

Ok this is a long story but here it goes:

I let my mother borrow my car while I fixed hers. She managed to not find 6 gear and only downshift into 4th unknowingly. She did this going 75mph for about 40 miles to work. At the end of the drive the car had a bad misfire and I had to come pick it up. I got down on it thinking it was a fouled plug and it cleared up, now for the strange part. On the ride home it started misfiring again going down the highway but I managed to make it home. Now it does it completely randomly. I'll drive one day and have no problems all the way through the rpm range and the next day it'll skip all through the rpm range. I'm lost. The optispark has like 5k on it as do the plug wires, plugs and coil. Any ideas?