Need to find AC DelCo E84 ECM Calib file checksum algorithm

[Cuongcoco Profile]

hi everyone.
i have Ecu AC Delco E84 for spark M400 and some file calib of this. now i need modify some byte on calib file but i can't not realize what is algorithm checksum of this file.
please help me find checksum fomular. thank you very much.

i have 3 file with 1 purpose 25202848, 25202950, 25202953. after i compare 3 file, i realize $08 -> $0b is length of this file - 12 byte, $0d-$0e maybe a checksum, $12-$15 is a name of file, and $28-$29 is CVN.
but i can't find how it calculate to check sum ( i tried not (sum 16 bit big ediant ) +1, or sometihing like this) but not success. i just want to change name of this calib file to name i want. please help me find it out. thank you very much.