Primes, cranks, fires, runs, and dies

[SchreinerM]

Hello all. Short story, it's a 2002 5.3L with NV4500 behind it. I did the harness using the LT1swap advice. Brendan reprogrammed the ECU. I popped a battery in the truck this evening and while it cranks and fires, it won't stay running. I'm looking for some advice on items to check. Here's the long story:

- With the battery in and the ignition on, the fuel pump primes just like my '02 Silverado.
- I pulled the injector fuses, hit the starter and it cranked over just like it should.
- After plugging the injector fuses in, it cranked and fired within a second. Good idle speed, definitely firing on all eight, very smooth.
- After 10-15 seconds, the idle speed slowed and the engine stopped.
- I keyed it off and back on, again the fuel pump kicked on right away. Assuming it was just air in the fuel lines, I hit the starter again and it fired right up. Same story at the first time, great idle speed and smooth running. But again, it died 10-15 seconds in.
- I repeated this process half a dozen times, all the same result where it died 10-15 seconds in.
- After about five start attempts I plugged in my cheap OBD2 code reader. With the ignition on, it did recognize the port and it had one code present P0102 - MAF). I cleared the code. From there on out, no codes were recorded.
- The next time after it fired I held the throttle partially open (cable throttle body) and it ran very smooth at ~2,000 RPM. Same result though, it died in under 20 seconds.
- In total I started it around 20 times, sometimes after it stalled I'd kick the ignition, some times not. Either way, it fired right back up afterward. On approximately five of the starts the idle speed slowed at the same time but the engine slowly stumbled to stalling out after around 25 seconds (like the engine wanted to stay running).
- No codes / CEL at this point.

Any smoking gun you guys suggest checking?