128K vs 256K Proms in one ecm

[Bruce Plecan]

Could some one splan to me why if the 739+749 use the same
PCB, why the 730 will not see a 128K prom, and a 749 sees 
either. 
730 using AUJP  749 using syclone campaign chip 
  On a 730 (92 Camaro), there is a 4th gear switch, that the ecm
"uses", anyone know for what?,  timing, fuel, TCC all seem the same
wiether it's on or off.
  There is a difference in TCC pinouts from 749 to 730.
The 730 basically leaves the EGR on all the time and flickers it once
in a while to test, it.  749 seems to not even flicker it, strange.

On the syclone idle if it's below 550 the IAC retracts, that's fine,
but as it exceeds 575 goin to a desired 600 the 600 jumps to 1250
anyone played with this??  Seems like would be lousy idling.
Bruce