My name is XXXXX XXXXX I will answer your question. If it is a electrical issue you should be able to perform a injector electrical test (buzz test) when cold and see if it sets any hard faults at that time. Unfortunatly the 7.3 will not do a cold cylinder baXXXXX XXXXXke you can with the 6.0 diesel. You can do a cylinder balance test, but engine oil has to be seen as hot to perform test. what you can to is install a 2K ohm resistor in place ot the oil temp sensor (unplug the sensor and put the resistor in the harness connector) to fool the pcm and run the balance test. this will tell you what cylinder is weak or missing. the only other way to do it is to cancel the injectors one at a time and this requires a special tool that is about $1500 and not a required dealer tool,most dealers do not have the tool.
with the mileage that you have on the truck I hope that they did cold and hot actual compression test of all the cylinder to make sure that none of them are weak when cold.