I'm wondering if you even found out what the issue was? I have exactly the same problem, tcm 15 with a k21 starts and runs fine for a couple seconds then shuts off. Occasionally blows the injector fuse. Only code is for fuel injector. It also reeks of propane after like it is running very rich. Tried swapping the injector and nothing. A different tech changed the fuel injector ecu and that fixed it but two weeks later it started doing exactly the same thing. Not sure where else to look