the problem is the timing it takes to silence the CCM module, which is the bus master on that particular car. as soon as you have power to it, the CCM and ECM both start blabbing away with useless information on the bus. the program needs to find a section of silence on that serial line (which has transmit and recieve on the same wire) long enough to throw out the necessary command, and complete sending it before more bus chatter happens.

what ADX are you using?

with tunerpro, the ADX isn't exactly smart enough to get the timing right, as far as I know, 'disconnecting and reconnecting' a few times usually does the trick, sometimes it might take a few tries.

of course i have to recommend eehack too, it's logging/analysis/graphing are purpose built for lt1 tuning and diagnosis.

it has a corvette-specific connection mode that apparently works well.. i didn't write the routine myself, someone with a corvette wrote it for me... it's been fairly well tested now. definitely give it a shot