Any Autotap parameter for it to show rear end gear ratio ? TIA

 

No, but you could fairly easily derive it from output shaft speed and vehicle speed (assuming you know tire height and which gear you happen to be in.)

 

Would that work if its programmed for 3:23s and it really has 3:42s in it?

 

I'm not sure what you mean. A couple of years ago I fooled around with stuff like to to prove that LS1-Edit was still having problems with C5 gear scaling (i.e. I needed to prove that the PCM still had knowledge of the old ratio somewhere. That issue is long since fixed.)

What exactly are you trying to do?