Tried to cal flash a modified tune into a 2014 Chevy truck with the 6.2 engine and OS #12663390. At the end of the flash got a "Script Exited with Code $06FF-Checksum Failure" . Engine would not crank or run. I then flashed the stock file back into it and it cranked and appears to be fine. Any ideas on what I need to do different or change?