Lack of cooling of the rear most cylinder could cause your proplem also. the rear most cylinder in an engine often runs the hottest also debris likes to collect in the coolant jacket around that cylinder. You got to find a cause or it will happen again. Something is wrong and you need to find it. as far as testing your injectors go, you pressurize the fuel rail and pulse each injector the same amount there is a tool that does this then you compare the pressure drop of each injector. also you see if the pressure bleeds of if it does there is a good change an injector is leaking.
