Dainslaif

So here's the deal. I finally hooked up my wideband gauge a few months ago, and ever since I did the car has always hovered around 14.3 AFR when not at WOT (where it drops down to 11.8 as it should). And I don't mean it goes from 14.3-15.1, I mean it goes from 13.9-14.7.

Mods:
60s, 2.9, K&N, catless 1.75/3" exhaust with Innovate LC-1 mounted at 3-O'clock.

It's not the O2 sensor (replaced with no effect, ST and LT fuel trims are displaying properly in HPT)
It's not the WB calibration (recalibrated with no effect)
It's not the tune (stoich is set to 14.7, fuel trims near 0)
It's possible that the WB is just reading off during cruise (haven't tried a new WB O2 or taken it to a dyno to test yet) but my tailpipe is pitch black and my car smells rich.

Does anyone know if there's any other possible cause? Could it be the O2 wiring to the PCM? Something I overlooked in the tune?

I'm going nuts here.

Dainslaif

Here's something to consider.

The thing that's confusing me is this; as I understand it, our car is supposed to go off the primary O2 to ensure that it is running within a certain air/fuel. It sees a certain AFR, calculates it against the RPM/MAF/MAP to determine how much fuel to put in during the next instant. Since it doesn't go off the O2 sensor during WOT, and my car appears to run the correct airfuel then, I'm thinking it's something wrong with something in the O2 system, but it's not the sensor itself.

Perhaps the increased radius of the header is making the O2 think it's running lean, so it adds more fuel than necessary, making it run rich? I'm just taking wild stabs at this point but now I'm curious if that even makes sense.