I would be very surprised if it was the coil pack. They tend to be reliable. Your sparkplug cable could be an issue---try swapping it with one on a different cylinder and see if the problem moves.
If you were low on oil pressure, I would think your problem would be most noticeable around town---at low rpm/low idle.
A bent or sticking valve would be a problem all the time, not just on the highway.
Low fuel pressure would cause a missfire at high speed, but it wouldn't happen on just one cylinder.
It seems most likely that your problem is electrically related....swap out the wire. Vastly cheaper and easier than messing with the coil packs. I notice that you have aftermarket cables....did you happen to save the old ones? If so, use on of those. If not, cylinder 1 and cylinder 5 probably have about the same length cables.
If you were low on oil pressure, I would think your problem would be most noticeable around town---at low rpm/low idle.
A bent or sticking valve would be a problem all the time, not just on the highway.
Low fuel pressure would cause a missfire at high speed, but it wouldn't happen on just one cylinder.
It seems most likely that your problem is electrically related....swap out the wire. Vastly cheaper and easier than messing with the coil packs. I notice that you have aftermarket cables....did you happen to save the old ones? If so, use on of those. If not, cylinder 1 and cylinder 5 probably have about the same length cables.
