Try it again once it's warmed up. Unlikely a bad injector is causing your low rail pressure, especially in a LBZ. 4.1 is borderline, but that doesn't mean much at cold engine.
It can actually cause rail issues... My LLY had 2 that were returning to much fuel but all 8 had perfect balance rates. Big tune would only hold 18k rail. Might not be this guys issue but can't be ruled out yet.
op we need more info on your truck, what do have done to it and what tuning?
It definitely can, but is much less common than other issues you'd expect in a LBZ. Balance rate also doesn't necessarily indicate high return flow rate... that's a separate test.
Before I went changing injectors because one is borderline, I would look at the CP3 and FPRV first.
Agreed, I think we are saying the same thing... My truck had 2 injectors returning way more than spec. but both had perfect balance rates. It would only hold 18k rail on the big tune with those 2 injectors being bad.