[hunter01]

I have the book for an 02 blazer and it has the same type of gear selector indicator. This is what I've been able to find.

PRNDL Display

The IPC (Instrument Panel Cluster) displays the selected gear position as determined by the PCM. (Powertrain Control Module)
The IPC recieves a class 2 message from the PCM indicating the gear position.

The PRNDL displays blank if:

-The PCM detects a malfunction in the transmission range switch circuit.

-The IPC recieves a class 2 message indicating the park position and the column park switch indicates a position other than park (open input)

-The IPC detects a loss of class 2 communications with the with the PCM.

That's all it says,I don't think this explains why it would be off by one but should give some indication as to how it works.