I read a series of posts a while back, on dieselplace.com, about some folks that were attempting to power an airboat with a Duramax. They were going to direct drive or use a gear reduction unit between the engine and propeller. It seems that they could not get the engine to run, because the Engine Control Module did not have a Transmission Control Module to "talk to". The ECM said in effect, "If I don't have a transmission, there's no point in me even starting". As I recall, no body could figure out how to "fool" the ECM into thinking it had a TCM connected to it. GM would offer no help, either.
Such is life in the age of computers.