PO171 & PO174 both banks lean 08 5.4 L

Both codes came AFTER all this…

Random loss of acceleration/stall/sputter original problem

Found 300 misfires on cylinder 1, so replaced coil.

Replaced all plugs.
Replaced fuel filter.

Can’t find vacuum leak at first glance but might be hard…I don’t understand if this is related to my original problem

I had this problem and same set of codes on my 03 5.4 just a couple week ago. The vacuum tree coming off the PCV valve had an elbow that was essentially rotten and more or less dissolved if you so much as brushed against it. I had a cyl 3 misfire with mine though this was directly above that coil/plug and when I removed lines to replace it all moisture came running out of it and right onto the coil. When I removed the coil there was light corrosion on the coil. I replaced it, inspected plug which was fine and good as new for the past few hundred miles.

If you disturbed any vacuum lines in that area while doing the work I would start there. I bought a smoke machine on Amazon to narrow my issue down as I wasn't sure where to start but I also have a couple other needs for it and the cost was more than justified to me. Fwiw I located my vacuum leak in less time than it took to unbox the machine. It made for VERY short diagnostic work and highly recommend if it's in your budget and can't quickly find your issue and you suspect it's vacuum related.