I own a 2003 dodge 3500 5.9L turbo with a 6speed tranny all stock. It has a code P0205 that keeps coming up. I am wondering if I will need to replace the injector or what?

 

usually its the injector but its always possible to be the wiring from the ECM to the injector or a ECM problem.
if you feel safe that its not a wiring issue throw an injector in it and call it a day.
take your valve cover off and inspect the wiring going to the number 5 injector for chaffing or shorts just to be safe