This just started the other day and am still stumped.
It seems to idle fine but when i get it on the road and up to speed (55) that is when you can really tell it is missing. The CEL will eventually flash a few times and then go off. When I got home I read the codes and got p0300 nad p0303.

The first thing I did was replace the spark plug in cylinder 3, but still have the issue.
When pulling the wire off of the spark plug while the truck was running, I get good spark from the wire so dont believe that is it. So I did not replace the spark plug wire.
I dont believe my truck has coil packs so nothing to replace there.

What would be my next step to try.

 

You have 2 coil packs - one for each group of 4 cylinders.

Doesn't really mean anything - it's only missing UNDER LOAD, right?

I'd advise you to replace all the plugs with MOTORCRAFT platinums and consider replacing the wire set with MOTORCRAFT wires. You MIGHT need a coil pack - the way to T/S that is swap the 2 of them, they are interchangeable.

 

Thanks for the information. I think I will try swapping out the coil packs to start and see what happens. I guess if the missing cylinder changes then I will know it is an issue with the coil pack.
Thanks for all of your help