I hate problems like this! Very tough.

First, you need to try a known good scanner. If the EFI tuner was able to communicate I can't think of any reason your scanner wouldn't, unless it's broken. Go back and forth between your vehicle and another with the same scanner. If it works on the other vehicle and not on yours repeatedly , that eliminates the scanner as a problem.

If the scanner is good and it still can't communicate with your ECM, you either have a wiring problem or an ECM problem. Do you have a CEL operational? On your ALDL port, check for good power and ground. Listen to your fuel tank--you may need a stethoscope if you have a very quiet fuel pump. Have a helper turn on the ignition without trying the starter. Do you get the fuel pump running for 2 seconds? If not That's either wiring or the ECM or the fuel pump. Since you have no scanner comm, I'd guess it wouldn't be the fuel pump...

You just have to be methodical and start ruling out different possibilities.

Good luck!