It's just a matter of what features are available. The later the rev letter (newer) the more features available.
I was trying to find some paperwork on what features were in the B chips, but haven't had much luck yet.
Rev. E/F which are the latest versions have an awful lot of features available, such as:
shift light (flashes SES light)
DFCO adjust for loose converters
Coolant fan temp control
cruise TCC lockup points
Lo Gear (1st and 2nd) WOT spark
System Shift (fuel curve)
Open or Closed loop idle
Lean cruise
Launch assist (timing retard)
WOT TCC lockup points
Spool fuel (richer or leaner)
Lo gear (1st and 2nd) WOT Fuel
All this plus anti theft and valet features!!
