Maybe I'm overthinking this. Engine: LS2 / E38 OS 12614676 ('07 Vette w/ 5L40E, which I understand is actually a Cal page typo since the Vette was a 6 speed). Trans: 4L60E / T42 OS 24239927 ('08 Silverado 4 speed auto). Is there a list somewhere indicating which ECM / TCM OS' are compatible? In this case, is the E38 confused because it is expecting to see a 6 speed T42; or does the E38 care? Is it necessary for the ECM / TCM to be from the same year or same body? Are the serial data / CAN protocols across all ECMs / TCMs compatible or not? Is there an OS reflash compatibility guide for the T42 (and I guess T43)?