Miss firing

I have a 1999 F250SD with a 5.4 liter engine. It idles fine but has a miss when under load. What should I be looking at? It has newer plugs and wires.

My guess is a vacuum leak as the first thing to look for if no codes and new plugs/wires.

You say plugs and wires. Doesn't that engine have COPs. Coil On Plugs?

From what I read a bad COP will cause your condition. There are 8 Coil On plugs, one on each spark plug.

A bad wire to an injector will also cause a misfire.