2002 GMC Sonoma GMC Sonoma Code P0301

About one every 4 to 5 months I get the code P0301, #1 cylinder misfire. It almost always sets when the truck is idling. The code clears after about 50 miles and then doesn't return for another 4-5 months. I've replaced the #1 spark plug with no change.

Also I read in the Shop Manual that this code is sometimes thrown for the automatic when it is traveling on a bumpy road and the crank shaft and cam shaft gets off. I do have a long bumpy driveway, but the code doesn't usually come as I'm driving down the drive. There is a slight misfire sound when it is idling.

Any clues as to where to look?

Doug Simmons