Time for another update. Unfortunately it makes me look ignorant but I wanted to post it up in case it helps someone else down the road.

My initial problem was that the engine would start then stall out after about a second. Instead of troubleshooting why, I immediately decided to delete VATS. That in and of itself isn't a bad thing. It will need to be eliminated eventually anyway when this engine gets transplanted. But after VATS was deleted it was still doing the same thing. That's when I decided I needed to troubleshoot.

It turns out it didn't take me long to figure out why the engine stalled out. If I'd have looked a bit closer when I purchased the truck I'd have seen it was missing the MAF sensor. I had a spare here so I put it in today and the engine started right up and stayed running. It isn't running "great" but it doesn't stall out. I will probably be flashing the original OS onto the PCM to see if it runs better before I spend much time doing any troubleshooting. If it does the same thing once the original .bin is flashed back I'll dig into it but that will be another thread if I need more help.

Thanks to everyone who took the time to respond to this thread.