I read the file out of a S10 with a 94 LT1/94PCM conversion. The PCM had been previously tuned by a tuner whose name I won't mention. I got an error message after the read saying the file had been modified and the checksum disabled. I emailed the file to Tunercat and they re-enabled the checksum and sent it back to me. Great customer service I must say. My question is why would a tuner disable the checksum? Was this some kind of attempt to lock the tune? Even with the checksum disabled, I was able to look at all the tables anyway. I was a little worried about flashing the file back into the PCM with it disabled though.