Injector cups

[4x4Acco]

Hi All, I'm sorry as this has assumably been covered before but I'm struggling to find the information I'm looking for. I have a Gen 2 Signature which has been quite sick for some time now. I am running out of things to check. I am trying to find out what the symptoms of leaking injector cups are? Im currently suffering really rough running under load, more load the more harsh it runs. Occasionally it seems like it partially hydraulic locks after being sitting for a few days. Doesn't actually lock completely but as you go to start it, cranks to a compression stroke, sounds like the battery is flat, then spins up like normal and usually starts. Sometimes it does that low voltage thing where it won't start, just turn off and start again and starts fine. Problem is out of the 90% of the time it runs shi#t, the other 10% it runs really smooth. Anyway was worried it has dropped a liner but not pushing water out like i would assume with a blown head gasket. Was worried it has a cracked head but not sure. Doesn't seem to use coolant like it has any major issue. Took a coolant sample to get tested. I flushed the system about 8 months ago with the fleet guard restore which seemed to work a treat. The new coolant (red) now looks like rusty water but not dark, just a light brown ish colour. No oil in coolant, no sludge in motor or under rocker cover...

Did an injector leak test as Rawze shows in the Video (Thanks mate, Top Job) no bubbles.

I guess I'm looking to find out what the cup actually does and if it fails and leaks, what can leak where???

Thanks in advance!