Suggest talking to the back counter or wholesale parts people at the dealerships, they work with the mechanics and the other shops in their area. You will find there are gaskets issues on this engine. Not the gaskets between the manifold and cyl head but the manifold and the intake plenium that the throttle body is bolted too.
On Fords, bank 1 is in your case cyls 1-3 and is the passenger side of the engine. Cyls 4-6 is the drivers side and is bank 2.
About 02 sensors, the sensor is telling you of an engine condition out of parameters and is throwing a code. If the sensor itself is out of spec it will print a code for that. Reread torkum's comment, it says it all. 02 sensors take a hit all to often when actually there are not defective.
My 02 4.2 is constructed with a different plenium and is affected by a TSB for the PO171 & PO174, Do what ever tests that you are capable of in looking for the intake leak that is causing the condition.
After complying with the TSB, I went 18 months with out a code being thrown, then I got a hit, PO174. It was very infrequent, like 2-3 weeks and would show its ugly self again. It eventually got worse, 2 or 3 days, then the cause showed itself completely with the brake booster failing. Special ordered the booster for the V-6 and replaced it. Its been 3 months and no more PO174. Point I'm try to make is, other things can affect an engine and the codes printed by the computor. Keep an open mind and proove or disproove every possibility.
Keep sucking Baby, this IS fun stuff.