[SpitAndDirt]

I have heard of the lifters starting to click with high mileage but not anything about them going completely out. Are you sure no one has been in there before you tampering with the rocker arms prior to your ownership of the truck? The reason that it started to miss is that the lifter could have had a piece of carbon stuck in it, and by tightening the rocker arm down, you may have dislodged it. You may need to go back in and readjust it. Possibly running a compression check on the motor. Ive got 157000 miles on my 96 z71 5.7L and no signs of major engine malfunction yet. I also am religious of oil changes and only use MOBIL 1 synthetic oil with ACDelco filter PF52. Occasionally I will substitute a quart of oil for a quart of Dexron III to help clean the inside of the motor. Hope this helps. -Chris