Yea, that is a mystery. I replaced the single pushrod and it runs like it did years ago again.
The only thing I can think is that the smog pump came apart so I deleted the smog pump, then the cat became clogged, like real clogged and the truck would bog and die and then it was like something in the cat was moving around because sometimes it would unclog but you never knew when. Then it backfired real hard one day. That's when the miss started.
Then I replaced the exhaust with flowmasters and for some reason the backfire seemed to have taken a map sensor out because it ran bad until I figured out the map sensor was bad. When I replaced the map sensor it ran dramatically better but always had a miss.
Now the miss is gone and it purrs through them flow masters.