Hi all. I've been chasing down a poor running '08 v8. This thing was a mess when I got it ( dealer screwed me, sight unseen ). Anyway its got 127k on it. This is what has been done by me, basically maintenance stuff:
Full tune up with oem parts
All vacuum lines replaced with OEM lines
Timing belt and pump done
Cleaned MAF and TB
rear cats deleted with URD y pipe
All 4 O2 sensors are original not replaced.

Here's my problem. It uses alot of gas compared to my '06 v8 and has a vibration at idle and higher RPM's. Put my scanner on it, short fuel trims both sides hover between -.07 - 1.5. Long term stays steady b1s1 -1.3, b2s1 +9.3. Those are too far apart. No vacuum leaks(tested with smoke machine). Voltages are within .2 of each other. I'm kinda leaning to a bad bank 2 O2 sensor. If so I would replace both. I just had the left exhaust manifold gasket replaced, and there is a very tiny crack in the manifold. Could the crack be causing the lean cond on bank 2 s1 O2 sensor?

I'd just remove and cap the vacuum lines attached to the intake (PCV, Vacuum Switching Valves...) and re-check LTFTs after some run time.

After this, I'd pull the spark plugs on Bank 2 and look for variation in burn coloration...indicating an injector or two underflowing.

If no leaks, and all plugs on Bank 2 are same burn coloration, then move on to the O2 sensor but use only a Denso or Toyota stock part. No Bosch or other manufacturers.