This is the exact issue I'm having. I did notice the old plugs had a different number on them than the new ones that went in. The new ones are ac delco iridium 41-103. I need help figuring this out.
A previous poster identified a coil pack as the problem. Swap a known good cylinder pack with the missing one and see if the problem changes cylinders. If it does you have your solution. If not, it could be as simple as a bad plug. In which case I would do the same with the plugs swap them and see if the issue moves with it. Process of elimination. The simplest solution is usually the right one. Good luck.