So I bought a scan tool.... pretty cool.....

2001 E150 v6

rough idle (seems rich)

p0171 system lean
p0174 system lean
p0304 misfire syslinder 4

guessing that means a bad coil on cylinder 4?

 

It's nice to know something is wrong, but just replacing parts can get expensive especially if you take the shotgun approach.
Why not consider this;
first swap the coi with another cyl and see if the misfire moves,
if it does your theory is good. If it still is on cyl 4 swap the plug and see if it moves.
If whichever move tells you it moved that , "could be the culprit".
Now what if you still have the misfire in cyl 4 ?
This is where the magic tool that tells you what to fix loses it's value.
Hopefully we might be able to help if you get to that roadblock.

If your scan tool provides other data like fuel trim , temp, etc., that is the info that might help pin down the cause/source of the problem.

 

 

They did have some problems with those coils and you are probably on the right track.
Sometimes you might see a crack for the tower for that cylinder. Give it a real close look for that.