I went to convert OS 1257603 to COS3 and it would take the FULL flash of the COS, it would take the calibration flash of the tune but then brick the pcm as soon as you try to read out the tune. It did this on 2 pcm's in the same truck one of which was a 100% stock before starting. I was able to recover one pcm with efi live and the used hp tuners and there 3 bar OS and it worked fine.