Stand pipes, dummy plugs, injector o rings... Sounds like a high pressure oil leak. Monitor your ICP while cranking. It needs to read at least 500psi for the engine to start.
You forgot to mention the notorious STC fitting.
The STC fitting connects the High Pressure Oil Pump (HPOP) to the high pressure oil system on the 05-up engines.
This fitting is more or less the same style fitting you would find on a shop airline. If you have been around any of them ever, you hear them leaking all the time.
The fitting fails internally over time and leaks. Sometimes the STC fitting will fail catastrophically and shoot out into (or through) the rear cover of the engine, but most times they stay intact and just leak like a sieve.
Being that your truck is an '06, and given the 100% failure rate of this fitting, my best internet mechanics' (
) guess is that this is likely the source of your problem. (been there myself already)
The replacement fitting (available HERE
) is a straight fitting and very reasonably priced.
Not too difficult of a job to do out in your driveway in an afternoon if you have a really good set of tools (metric and ASE wrenches, sockets, swivels etc).
That huge beast under the hood only appears intimidating the first time you wrench on it. It isn't nearly as bad as you think.