So help me clarify your current problem,
Originally it had one dead bank and you found a melted plug. You’ve fixed the melted connector and are absolutely sure there are no wiring or connection issues under the valve cover or in the valve cover gasket plug or in the engine harness plugs? You had it code read and found two seemingly unrelated codes? The truck now runs but has a slight miss? Have you cleared the codes and seen if any beside 603 come back? Do you have access to a spare IDM you could try? How much have you tried to run the truck and how bad does the miss seem.