Hello Jimmy
In this Optima, based on autohex fault codes, the P0303: Cylinder 3 -misfire detected
You almost did all possible replacments, please check using Autohex the following:

Since Optima 4 Cyl engines they don't have activation for coils ( for Engines like:2.7L V6 GASOLINE ,2.6L V6 GASOLINE ,2.5L V6 GASOLINE  they have), we will test the Injector No.3
After you enter the correct Ecu type (in Optima 2004 you have exactly 10 different types):
1- Select Actuations
2- From Actuations, select "INJECTOR-CYL.3"
3- Follow conditions (Engine ON)
4- Turn the Injector off by clicking on "OFF" button in the Autohex

If you feel the engine starts struggling, then the injector stops so the cylinder stoped, which means, the wire/spark plug,... and injetctor are fine, the problem could have many reasons like:
1- sometimes while driving this error comes because some bad wire connetion (especially the earth of coils)
2- the Cyilender 3 is leaking some oil to the spark plug
3- weak connection Ecu wires to the coils
4- Ecu mulfunction

if this actuation did not work, either the injector is not plusing already (before the test is already off), or it is not responding, I will doubt in ECU wiring or Ecu itself.