P0171 P0174 codes, unable to find air (vacuum) leak

2007 Expedition 5.4L 3V 320k miles

After a recent fuel up, a CEL was set. Codes were P0171 and P0174, lean bank 1 and bank 2. Trans is shifting hard and delayed. Long term fuel trims were maxed out at >29% for each back. I assume a loose gas cap so I check it (the rubber O-ring seems fine), retighten the cap, clear codes, go for a drive. A bit later, the CEL comes back with the same codes, same hard shifting problems.

I assume a vacuum leak so I do a smoke test. I disconnected the vac line at the brake booster and inject smoke into the intake manifold. I find a tiny leak at the vacuum line for the 4WD solenoid, which I fix. Smoke is pouring out the air filter airbox, so I plug the air intake line. No signs of smoke anywhere in the engine bay. I then inject smoke into the intake manifold above the throttle body. Again, no smoke is leaking out anywhere.

Some days later, I get a CEL for low fuel pressure. I had this code a few years ago and changed out the fuel filter. I do the same thing now. The supply side of the fuel line (from the tank & pump) is filthy dirty. The shifting problems go away for 30 miles and then come back.

This weekend I checked the fuel pressure after an overnight sit. Initial pressure was about 7 psi (KOEO), then climbed to 38 quickly once the engine was started. Pressure drops to about 28-30 psi with WOT. Both of these ranges or numbers seem inline with what's normal. I assume that my fuel pump and filter are working as designed.

The CEL and hard shifting have been a problem for roughly 75 gallons of fuel, so I assume that fuel QUALITY is not an issue.

What do I check next? Lean on both banks should indicate something on the intake side of the engine, but I can't find the leak.

Another interesting observation is that after an oil change last week, the sample was sent off to Blackstone for testing. It showed high iron, aluminum, and silicon, which were high at the last oil change, too (so, roughly 15,000 miles altogether). High silicon usually come from new gaskets or ingesting dirty air. High silicon from dirt frequently causes high iron and aluminum. Ingesting dirty, unmetered air will cause a lean condition. But where is this air leak?