sorry i deleted my post, i didn't realize this was LS1 :doh:
After checking the LS1 code (previously i had only checked the later code).
Here's everything that disables the misfire test:
RPM thresholds
ECT thresholds
IGNV thresholds
Throttle faults
IAT fault
MAF fault
MAP fault
VSS fault
ECT fault
Cam Sensor fault
Crank Sensor Fault
If Misfires are detected while the TCC is locked (and susequently unlocked)
If crank position is not learned
very cold startup
PTO is engaged
The list is very similar to the later vehicles, they just have more requirements!
Chris...