Tuning help needed - '91 TBI 383 w/ Vortec heads

[Kitch]

I've been wondering for ages what was causing my spark timing to bounce around at idle so much!
It would be much appreciated if you could give me an example of how your tables vary from my stock ones (shown in the attachment).
I'm keen to try this out :-)

[donf]

Idle Overspeed Spark Retard vs. RPM Error 0.0 0.0 0.0 0.0 1.1 2.1 3.2
Idle Underspeed Spark Advance vs. RPM Error 0.0 0.0 0.0 0.0 2.1 2.1 3.2
It's not my tip, someone that is very familiar with the later LS computers told me to check that when I was wondering why the timing was so unstable at idle. My $0D computer has it, not sure about the earlier ones.