Try checking you rocker arms, they may have gotten loose over the time that you have had the truck. I had a 350 that had a loss of power ran good at idle, and had a tapping sound and it was the #3 rocker arms were a little loose. I tightened them back up and its run fine ever since. You may want to check the plugs that the wires were burnt off of too, they maybe fouling.
Hope this helps you out