Just like the 7.3L, your injectors fire off of high pressure oil. You need to monitor the high pressure oil system pressure. We will also need to see some other engine parameters when running and when cranking.
Also, you need to tell us what year truck it is. If it is an 04, you need to tell us where the ICP
For a monitor, you can get a scangaugeII already programmed for our trucks, DieselTechRon has a video out on using them. You can also get a smartphone app and an OBDII ELM327 adapter. I like Torque Pro or ForScan Lite and I like the BAFX adapters. Use a WiFi adapter if you have an i-phone and a Bluetooth adapter if you have Android. Download the app to your phone and get going. You HAVE TO HAVE a monitor or you will continue to throw money and parts at it.
When you get the monitor, we need to see ICP
voltage and ICP
pressure, and IPR
% duty cycle - with KOEO
, when cranking, and at cold and hot idle.
In the meantime, you can do some searches for DieselTechRon videos on doing an air test of the high pressure oil system.
It would also help us to know what oil you are using, what oil and fuel filters you use, whether or not your oil filter cap is OEM, how old the oil is, and whether or not you are low or high on the dipstick.
Another test that may be helpful is the bubble test (fuel), since you apparently have at least one injector issue.
Eventually, you need to consider adding on a fuel pressure sensor and gauge. Low fuel pressure can damage expensive injectors. You can have low fuel pressure from a bad regulator (ie your new fuel pump may not be getting the pressure you need to the injectors). In fact, International and Ford sell an updated spring for the fuel pressure regulator because the OEM spring weakened and couldn't properly hold an adequate pressure. I think you can wait a while on this gauge though, it seems more like a HPO issue at this point.