2001 F150 build

have you checked fuel pressure while drivin? I had a truck that would test fine idleing/revving sitting still but lost pressure going down the road.

I been working on my kids 5.4l expedition, got some knowledge lately, LOL. The knock in the motor, when the coil packs stop working for some reason the lifters collapse and knocks on that dead cylinder while driving or reving in park but sounds ok idling. Can loosen the manifolds to see it that helps, to check if cats are plugged but don't think so. I would focus on the coil packs and spark plugs for the loss of power, pretty common problem with these engines, along with vacuum leaks. Ford used crappy vacuum lines and they go bad easily. If you got a scanner that can read live data, that helped out a lot with me on the Expedition of my kids. ScannerDanner is pretty good on YouTube and does a lot of these trucks, LOL.

Has new plugs. Ideally I’d do a power balance test and figure out exactly what cylinder it is. Because it DEFINITELY has a miss