If your thoughts are injector.... here is what GM has to say on it... found it in this cool PDF doing some searching:
Balancing Rates
This will show the amount of fuel being added to or taken
away from each cylinder during normal idling. Normal fuel delivery
to each cylinder is around 1 cubic millimeter (mm3) for the
pilot injection and 7 mm3 for the main injection.
Balancing rates are available only during idle. These numbers
tell you whether or not you have a possible compression problem
or possibly an injector that is stuck open or closed.
Once the misfire is detected, the balancing rate of the cylinder
that has the miss will be slightly higher in mm3, or may be
as high as 12 mm3. The misfire codes (P0300s) will set only in
the first 90 seconds of engine operation and will set only when
the balancing rate of the “missing” cylinder goes above 7 mm3.
The normal values that should be seen on the balancing rate
screen will range between -2.4 and +2.4. These numbers will
move around constantly, based on the crankshaft speed.
Suspect a possible problem when the balancing rate of a particular
cylinder starts to go up in mm3. An example of a possible
problem cylinder would be a balancing rate of 5 mm3 or so.
Once the numbers start to creep up, the cylinder is progressively
getting worse in performance.
Link to PDF:
http://www.norcal-cobras.com/GTM/gm-tech-link/7_01_e.pdf