Shaking F250

[tjs4x4]

My neighbor has a F250 that the engine is really shaking back and forth, he said he replaced the spark plugs but is not sure what else it could be. The idle seems to be holding steady, and he fixed a vacuum leak. What else could it be?

 

[prerunner]

Have him (or her) check their firing order. They might have 2 plug wires misplaced. Is there a code?

 

[tjs4x4]

He had two spark plug wires crossed apparently LOL.