For the record....never sat in a Blackhawk but once at an Airshow and know naught of how they work.
Years of flying the Cninook taught me a few things about diagnosing engine problems....and adhering to the KISS method works the best.
Basic Assumption is you have not moved the Collective (Thrust Lever in real helicopters)...and in your bi-hourly cross check of the engine/rotor gauges....you notice a deviation from Normal.
High Nr....can only mean one thing.....it is a high side failure of some kind.
Low or Normal Nr with split indications mean it can be either a Low Side problem or a Static problem.
A split in Torque or Exhaust Temp or Gas Producer or Power Turbine.....is an indication of a problem....not what the problem is.
If one starts with the Nr....then casts an Eagle Eye through your Aviator Ray Bans to assess where all the other gauges are resting.....and compare the indications to the "normal ranges" the engines are supposed to operate at....you can begin to sort out what is going on.
Bottom line....if you move the Collective (or Thrust Lever)....in an ideal world both engines will respond in a normal manner and the Nr would remain constant. If one engine is reacting normally....and the other isn't.....the KISS method states the one that is not reacting normally is the problem child.
There is no need to move an Engine Lever/Speed Select/throttle until after doing the Collective Check (IMHO). Odds are....if you check with Collective first....you will get the correct Engine Lever on the first go....rather than having a 50% chance of getting the wrong one (assuming you can remember to keep the two things sorted out as to which is #1 and the other is #2....Port and Starboard for the Navy and Coasties....or however the Zoomies do it.
I would also suggest livening up a Safety Meeting with StanEval by asking why you even want to move things and shut things off if the Nr is in the right range as if one does nothing....one does not do anything wrong. (Assuming a very short flight to a safe landing spot.....then sort stuff out on the ground).