There was a bad batch of valve springs from mid 1997 to early 1999 in both 4 and 6cyl engines.
It should have been a recall with the number of vehicles it effected. Instead it's no more than a TSB. The TSB basically states that if you suffer from a recurring misfire after verifying the ignition & fuel systems are properly operating, then it is likely a week valve spring, and the head should be removed for overhaul.
With the availability of tools today, a tech can replace the valve springs without removing the head! No need to perform the expensive overhaul, or replace the head, just replace the faulty parts!