Brief summary:

Truck has a locked, working, EFI tuned DSP5 ECM in it. Purchased EFI and tunes from same tuner, was planning to load on to a spare ECM so I could make changes.

Acquired spare ECM, installed into truck, no start (I expected this with a different VIN), FULL flashed a stock tune with the correct VIN on it. Still no start.

Ideas?