Take the valve cover off, you have a rocker arm that fell off and you are riding on 7 cylinders. This happened to me last month i have a ram 1500 with 174k same 4.7 engine. Done deal. Stop shotgun troubleshooting and blowing money on crap that wont fit your problem.
I went through all the same spark plug, coil crap with no positive response only mo wasted $$. I even checked the plugs after i replaced them and #3 was all black it's because the value is not working. So this sounds very familiar.
Now you need to get a miller tool #8387 or 8516 (check by calling miller) about 60 bucks from Miller direct, all others mark it up 30%. You need this to help you compress the spring and insert the rocker arm. The shop will charge you $650 to do this and that's the usual rip off dealer. Dont buy till you verify. (sounds cool)
My suggestion is to replace the rocker arm, and lash adjuster at the same time rocker arm is $14, lash $6. I compared the old rocker arm with the new one and the bearing rolls easy new, but slugish on the old one.
You also need a haynes manual or equivalent. You can do this your self in about 2-1/2 hours or get your GF to do it.
But the questions is what is the root cause for this to happen? I have read several threads, talked to experts, etc. Don't know the answer.
My theory is that oil varnish builds up even if you get oil changed every 3k miles. This sticky build up is too much for the engineer to overcome in their less than stellar robust design. Several mechanics swear to BG MOA additive to help reduce the varnish. Sounds like Im pissed? You bet I am, I never had these issues with my 69 mustang, seemed simple back then, but now it's all different.